Solution & Explanation
### Related Formula
textWhen powers of sine and cosine add up to a negative even integer, extract sec^2 x text and substitute tan x = t$$\text{When powers of sine and cosine add up to a negative even integer, extract } \sec^2 x \text{ and substitute } \tan x = t$$
### Core Logic
Integral: I = int sin^-11/2 x cos^-5/2 x \, dx$I = \int \sin^{-11/2} x \cos^{-5/2} x \, dx$
The sum of powers is -frac112 - frac52 = -8$-\frac{11}{2} - \frac{5}{2} = -8$.
Convert the integrand entirely into terms of tan x$\tan x$ and sec x$\sec x$ by dividing and multiplying by cos^-11/2 x$\cos^{-11/2} x$.
I = int left(fracsin xcos xright)^-11/2 cos^-11/2 x cos^-5/2 x \, dx$$I = \int \left(\frac{\sin x}{\cos x}\right)^{-11/2} \cos^{-11/2} x \cos^{-5/2} x \, dx$$
I = int (tan x)^-11/2 (cos x)^-8 \, dx$$I = \int (\tan x)^{-11/2} (\cos x)^{-8} \, dx$$
I = int (tan x)^-11/2 sec^8 x \, dx$$I = \int (\tan x)^{-11/2} \sec^8 x \, dx$$
### Step 1: Integration by Substitution
Rewrite sec^8 x = (sec^2 x)^3 sec^2 x = (1 + tan^2 x)^3 sec^2 x$\sec^8 x = (\sec^2 x)^3 \sec^2 x = (1 + \tan^2 x)^3 \sec^2 x$.
I = int (tan x)^-11/2 (1 + tan^2 x)^3 sec^2 x \, dx$$I = \int (\tan x)^{-11/2} (1 + \tan^2 x)^3 \sec^2 x \, dx$$
Substitute t = tan x implies dt = sec^2 x \, dx$t = \tan x \implies dt = \sec^2 x \, dx$.
I = int t^-11/2 (1 + t^2)^3 \, dt$$I = \int t^{-11/2} (1 + t^2)^3 \, dt$$
Expand (1 + t^2)^3 = 1 + 3t^2 + 3t^4 + t^6$(1 + t^2)^3 = 1 + 3t^2 + 3t^4 + t^6$.
I = int t^-11/2 (1 + 3t^2 + 3t^4 + t^6) \, dt$$I = \int t^{-11/2} (1 + 3t^2 + 3t^4 + t^6) \, dt$$
I = int (t^-11/2 + 3t^-7/2 + 3t^-3/2 + t^1/2) \, dt$$I = \int (t^{-11/2} + 3t^{-7/2} + 3t^{-3/2} + t^{1/2}) \, dt$$
### Step 2: Evaluating the Anti-derivatives
Integrate term by term:
I = fract^-9/2-9/2 + 3fract^-5/2-5/2 + 3fract^-1/2-1/2 + fract^3/23/2 + C$$I = \frac{t^{-9/2}}{-9/2} + 3\frac{t^{-5/2}}{-5/2} + 3\frac{t^{-1/2}}{-1/2} + \frac{t^{3/2}}{3/2} + C$$
I = -frac29t^-9/2 - frac65t^-5/2 - 6t^-1/2 + frac23t^3/2 + C$$I = -\frac{2}{9}t^{-9/2} - \frac{6}{5}t^{-5/2} - 6t^{-1/2} + \frac{2}{3}t^{3/2} + C$$
Substitute back t = tan x = frac1cot x$t = \tan x = \frac{1}{\cot x}$, which implies t^-a = (cot x)^a$t^{-a} = (\cot x)^a$.
I = -frac29(cot x)^9/2 - frac65(cot x)^5/2 - frac61(cot x)^1/2 + frac23(cot x)^-3/2 + C$$I = -\frac{2}{9}(\cot x)^{9/2} - \frac{6}{5}(\cot x)^{5/2} - \frac{6}{1}(\cot x)^{1/2} + \frac{2}{3}(\cot x)^{-3/2} + C$$
### Step 3: Variable Assignment
Comparing with -fracp_1q_1(cot x)^9/2 - fracp_2q_2(cot x)^5/2 - fracp_3q_3(cot x)^1/2 + fracp_4q_4(cot x)^-3/2$-\frac{p_1}{q_1}(\cot x)^{9/2} - \frac{p_2}{q_2}(\cot x)^{5/2} - \frac{p_3}{q_3}(\cot x)^{1/2} + \frac{p_4}{q_4}(\cot x)^{-3/2}$:
p_1 = 2, q_1 = 9$p_1 = 2, q_1 = 9$
p_2 = 6, q_2 = 5$p_2 = 6, q_2 = 5$
p_3 = 6, q_3 = 1$p_3 = 6, q_3 = 1$
p_4 = 2, q_4 = 3$p_4 = 2, q_4 = 3$
Calculate frac15 p_1 p_2 p_3 p_4q_1 q_2 q_3 q_4$\frac{15 p_1 p_2 p_3 p_4}{q_1 q_2 q_3 q_4}$:
= frac15(2)(6)(6)(2)(9)(5)(1)(3) = frac15 times 144135 = frac2160135 = 16$$= \frac{15(2)(6)(6)(2)}{(9)(5)(1)(3)} = \frac{15 \times 144}{135} = \frac{2160}{135} = 16$$
### Pattern Recognition
If int sin^m x cos^n x \,dx$\int \sin^m x \cos^n x \,dx$ has m+n$m+n$ as a negative even integer, unconditionally extract sec^|m+n|x$\sec^{|m+n|}x$ and set tan x = t$\tan x = t$. The expansion expands gracefully into polynomial power rules without any trig substitution hassle.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Maths: Indefinite Integration
More Indefinite Integration Previous-Year Questions
Q57
jee_main_2025_02_april_evening
Properties of Definite Integrals
Let (a, b)$(a, b)$ be the point of intersection of the curve x^2 = 2y$x^2 = 2y$ and the straight line y - 2x - 6 = 0$y - 2x - 6 = 0$ in the second quadrant. Then the integral I = int_a^b frac9x^21 + 5^x \, dx$I = \int_{a}^{b} \frac{9x^2}{1 + 5^x} \, dx$ is equal to:
Solution
### Related Formula
textKing's Property: int_a^b f(x) dx = int_a^b f(a+b-x) dx$$\text{King's Property: } \int_{a}^{b} f(x) dx = \int_{a}^{b} f(a+b-x) dx$$
### Core Logic
First, we find the coordinates of intersection in the second quadrant to determine the integration limits a$a$ and b$b$.
### Step 1: Find points of intersection
Substitute y = fracx^22$y = \frac{x^2}{2}$ into the line equation y - 2x - 6 = 0$y - 2x - 6 = 0$:
fracx^22 - 2x - 6 = 0 implies x^2 - 4x - 12 = 0$$\frac{x^2}{2} - 2x - 6 = 0 \implies x^2 - 4x - 12 = 0$$
(x - 6)(x + 2) = 0 implies x = 6 quad textor quad x = -2$$(x - 6)(x + 2) = 0 \implies x = 6 \quad \text{or} \quad x = -2$$
Since the point (a, b)$(a, b)$ lies in the second quadrant, x$x$ must be negative:
a = -2$a = -2$
b = 2(a) + 6 = 2(-2) + 6 = 2$$b = 2(a) + 6 = 2(-2) + 6 = 2$$
Thus, the integration limits are a = -2$a = -2$ and b = 2$b = 2$.
### Step 2: Solve the Integral using King's Property
The integral is:
I = int_-2^2 frac9x^21 + 5^x dx quad text--- (1)$$I = \int_{-2}^{2} \frac{9x^2}{1 + 5^x} dx \quad \text{--- (1)}$$
Apply King's property, substituting x to -x$x \to -x$ (since -2 + 2 - x = -x$-2 + 2 - x = -x$):
I = int_-2^2 frac9(-x)^21 + 5^-x dx = int_-2^2 frac9x^2 cdot 5^x1 + 5^x dx quad text--- (2)$$I = \int_{-2}^{2} \frac{9(-x)^2}{1 + 5^{-x}} dx = \int_{-2}^{2} \frac{9x^2 \cdot 5^x}{1 + 5^x} dx \quad \text{--- (2)}$$
Adding equations (1) and (2):
2I = int_-2^2 9x^2 left( frac1 + 5^x1 + 5^x right) dx = int_-2^2 9x^2 dx$$2I = \int_{-2}^{2} 9x^2 \left( \frac{1 + 5^x}{1 + 5^x} \right) dx = \int_{-2}^{2} 9x^2 dx$$
Since 9x^2$9x^2$ is an even function:
2I = 2 int_0^2 9x^2 dx implies I = left[ 3x^3 right]_0^2 = 3(8) - 0 = 24$$2I = 2 \int_{0}^{2} 9x^2 dx \implies I = \left[ 3x^3 \right]_{0}^{2} = 3(8) - 0 = 24$$
### Pattern Recognition
Whenever you see an exponential denominator like 1 + c^x$1 + c^x$ inside a symmetric interval definite integral [-a, a]$[-a, a]$, applying King's property will almost always cancel the exponential factor cleanly when the remaining numerator is even.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Mathematics: Integral Calculus
Q63
jee_main_2025_02_april_evening
Integration by Rationalisation
4int_0^1left(frac1sqrt3 + x^2 + sqrt1 + x^2right)mathrmdx - 3log_eleft(sqrt3right)$4\int_{0}^{1}\left(\frac{1}{\sqrt{3 + x^2} + \sqrt{1 + x^2}}\right)\mathrm{d}x - 3\log_{e}\left(\sqrt{3}\right)$ is equal to:
- A. 2 + sqrt2 + log_mathrmeleft(1 + sqrt2right)$2 + \sqrt{2} + \log_{\mathrm{e}}\left(1 + \sqrt{2}\right)$
- B. 2 - sqrt2 - log_mathrmeleft(1 + sqrt2right)$2 - \sqrt{2} - \log_{\mathrm{e}}\left(1 + \sqrt{2}\right)$
- C. 2 + sqrt2 - log_mathrmeleft(1 + sqrt2right)$2 + \sqrt{2} - \log_{\mathrm{e}}\left(1 + \sqrt{2}\right)$
- D. 2 - sqrt2 + log_mathrmeleft(1 + sqrt2right)$2 - \sqrt{2} + \log_{\mathrm{e}}\left(1 + \sqrt{2}\right)$
Solution
### Related Formula
int sqrta^2 + x^2 dx = fracx2 sqrta^2 + x^2 + fraca^22 lnleft| x + sqrta^2 + x^2 right|$$\int \sqrt{a^2 + x^2} dx = \frac{x}{2} \sqrt{a^2 + x^2} + \frac{a^2}{2} \ln\left| x + \sqrt{a^2 + x^2} \right|$$
### Core Logic
We first rationalise the denominator to split the integral into two standard integration terms.
### Step 1: Rationalise the integrand
Multiply the numerator and denominator by sqrt3+x^2 - sqrt1+x^2$\sqrt{3+x^2} - \sqrt{1+x^2}$:
frac1sqrt3 + x^2 + sqrt1 + x^2 = fracsqrt3 + x^2 - sqrt1 + x^2(3+x^2) - (1+x^2) = fracsqrt3 + x^2 - sqrt1 + x^22$$\frac{1}{\sqrt{3 + x^2} + \sqrt{1 + x^2}} = \frac{\sqrt{3 + x^2} - \sqrt{1 + x^2}}{(3+x^2) - (1+x^2)} = \frac{\sqrt{3 + x^2} - \sqrt{1 + x^2}}{2}$$
Thus, the integral expression simplifies to:
I = 4 int_0^1 left( fracsqrt3 + x^2 - sqrt1 + x^22 right) dx - 3log_eleft(sqrt3right)$$I = 4 \int_{0}^{1} \left( \frac{\sqrt{3 + x^2} - \sqrt{1 + x^2}}{2} \right) dx - 3\log_{e}\left(\sqrt{3}\right)$$
I = 2 int_0^1 sqrt3 + x^2 dx - 2 int_0^1 sqrt1 + x^2 dx - frac32 log_e 3$$I = 2 \int_{0}^{1} \sqrt{3 + x^2} dx - 2 \int_{0}^{1} \sqrt{1 + x^2} dx - \frac{3}{2} \log_{e} 3$$
### Step 2: Evaluate the integrals
For the first integral:
2 int_0^1 sqrt3 + x^2 dx = 2 left[ fracx2 sqrt3 + x^2 + frac32 lnleft| x + sqrt3 + x^2 right| right]_0^1$$2 \int_{0}^{1} \sqrt{3 + x^2} dx = 2 \left[ \frac{x}{2} \sqrt{3 + x^2} + \frac{3}{2} \ln\left| x + \sqrt{3 + x^2} \right| \right]_{0}^{1}$$
= left[ x sqrt3 + x^2 + 3 lnleft| x + sqrt3 + x^2 right| right]_0^1$$= \left[ x \sqrt{3 + x^2} + 3 \ln\left| x + \sqrt{3 + x^2} \right| \right]_{0}^{1}$$
= left( sqrt4 + 3 ln(1 + sqrt4) right) - left( 0 + 3 lnsqrt3 right)$$= \left( \sqrt{4} + 3 \ln(1 + \sqrt{4}) \right) - \left( 0 + 3 \ln\sqrt{3} \right)$$
= 2 + 3 ln 3 - frac32 ln 3 = 2 + frac32 ln 3$$= 2 + 3 \ln 3 - \frac{3}{2} \ln 3 = 2 + \frac{3}{2} \ln 3$$
For the second integral:
-2 int_0^1 sqrt1 + x^2 dx = -2 left[ fracx2 sqrt1 + x^2 + frac12 lnleft| x + sqrt1 + x^2 right| right]_0^1$$-2 \int_{0}^{1} \sqrt{1 + x^2} dx = -2 \left[ \frac{x}{2} \sqrt{1 + x^2} + \frac{1}{2} \ln\left| x + \sqrt{1 + x^2} \right| \right]_{0}^{1}$$
= - left[ x sqrt1 + x^2 + lnleft| x + sqrt1 + x^2 right| right]_0^1$$= - \left[ x \sqrt{1 + x^2} + \ln\left| x + \sqrt{1 + x^2} \right| \right]_{0}^{1}$$
= - left( sqrt2 + ln(1 + sqrt2) right)$$= - \left( \sqrt{2} + \ln(1 + \sqrt{2}) \right)$$
### Step 3: Sum the terms
Now compile all terms:
I = left( 2 + frac32 ln 3 right) - sqrt2 - ln(1 + sqrt2) - frac32 ln 3$$I = \left( 2 + \frac{3}{2} \ln 3 \right) - \sqrt{2} - \ln(1 + \sqrt{2}) - \frac{3}{2} \ln 3$$
I = 2 - sqrt2 - ln(1 + sqrt2)$$I = 2 - \sqrt{2} - \ln(1 + \sqrt{2})$$
### Pattern Recognition
Integration of roots of quadratics: Always look for algebraic rationalisation when dealing with sum of root denominators. It directly reduces complex fractions into standard integrable functions.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Mathematics: Integral Calculus
Q71
jee_main_2025_02_april_morning
Definite Integration with GIF
Let [cdot]$[\cdot]$ denote the greatest integer function. If int_0^e^3left[frac1e^x - 1right]mathrmdx = alpha -log_e2$\int_{0}^{e^{3}}\left[\frac{1}{e^{x - 1}}\right]\mathrm{d}x = \alpha -\log_{e}2$, then alpha^3$\alpha^3$ is equal to ________.
Numerical Answer. Answer: 8 to 8
Solution
### Related Formula
Greatest Integer Function boundaries:
[f(x)] = k quad textfor quad k le f(x) < k+1, \ k in mathbbZ$$[f(x)] = k \quad \text{for} \quad k \le f(x) < k+1, \ k \in \mathbb{Z}$$
### Core Logic
Analyze the value variations of f(x) = e^1-x$f(x) = e^{1-x}$ across the integration limits [0, e^3]$[0, e^3]$ to break down the integral into distinct piecewise continuous intervals.
### Step 1: Determine Step Function Transition Points
Let y = e^1-x$y = e^{1-x}$.
* At x = 0 implies y = e^1 approx 2.718$x = 0 \implies y = e^1 \approx 2.718$
* As x$x$ increases, e^1-x$e^{1-x}$ decreases monotonically.
* Find x$x$ where y = 2 implies e^1-x = 2 implies 1-x = ln 2 implies x = 1 - ln 2$y = 2 \implies e^{1-x} = 2 \implies 1-x = \ln 2 \implies x = 1 - \ln 2$.
* Find x$x$ where y = 1 implies e^1-x = 1 implies 1-x = 0 implies x = 1$y = 1 \implies e^{1-x} = 1 \implies 1-x = 0 \implies x = 1$.
* At the final boundary x = e^3 implies y = e^1-e^3$x = e^3 \implies y = e^{1-e^3}$, which is a very small positive decimal strictly inside (0,1)$(0,1)$.
### Step 2: Split the Definite Integral
Rewrite the integral based on the isolated interval blocks:
I = int_0^1-ln 2 2 \, mathrmdx + int_1-ln 2^1 1 \, mathrmdx + int_1^e^3 0 \, mathrmdx$$I = \int_{0}^{1-\ln 2} 2 \, \mathrm{d}x + \int_{1-\ln 2}^{1} 1 \, \mathrm{d}x + \int_{1}^{e^3} 0 \, \mathrm{d}x$$
### Step 3: Perform Integrations
I = 2[x]_0^1-ln 2 + 1[x]_1-ln 2^1 + 0$$I = 2[x]_0^{1-\ln 2} + 1[x]_{1-\ln 2}^{1} + 0$$
I = 2(1 - ln 2 - 0) + 1(1 - (1 - ln 2)) = 2 - 2ln 2 + ln 2 = 2 - ln 2$$I = 2(1 - \ln 2 - 0) + 1(1 - (1 - \ln 2)) = 2 - 2\ln 2 + \ln 2 = 2 - \ln 2$$
### Step 4: Solve for Alpha Cubed
Compare the integrated value to alpha - ln 2$\alpha - \ln 2$:
alpha - ln 2 = 2 - ln 2 implies alpha = 2$$\alpha - \ln 2 = 2 - \ln 2 \implies \alpha = 2$$
alpha^3 = 2^3 = 8$$\alpha^3 = 2^3 = 8$$
### Pattern Recognition
Always map the function values at the extreme boundary points first. Tracking the downward path from 2.71 rightarrow 2 rightarrow 1 rightarrow 0$2.71 \rightarrow 2 \rightarrow 1 \rightarrow 0$ reveals exactly where the integer thresholds are crossed.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Mathematics: Integrals
Q59
jee_main_2025_03_april_evening
Definite Integrals
The integral int_0^pi frac8x \, dx4cos^2 x + sin^2 x$\int_0^\pi \frac{8x \, dx}{4\cos^2 x + \sin^2 x}$ is equal to
- A. 2pi^2$2\pi^2$
- B. 4pi^2$4\pi^2$
- C. pi^2$\pi^2$
- D. frac3pi^22$\frac{3\pi^2}{2}$
Solution
### Related Formula
Using the properties of definite integrals:
int_a^b f(x) \, dx = int_a^b f(a+b-x) \, dx$$\int_a^b f(x) \, dx = \int_a^b f(a+b-x) \, dx$$
Also, if f(2a-x) = f(x)$f(2a-x) = f(x)$, then:
int_0^2a f(x) \, dx = 2 int_0^a f(x) \, dx$$\int_0^{2a} f(x) \, dx = 2 \int_0^a f(x) \, dx$$
### Core Logic
Let:
I = int_0^pi frac8x \, dx4cos^2 x + sin^2 x quad text--- (1)$$I = \int_0^\pi \frac{8x \, dx}{4\cos^2 x + \sin^2 x} \quad \text{--- (1)}$$
Applying x to pi-x$x \to \pi-x$:
I = int_0^pi frac8(pi - x) \, dx4cos^2 x + sin^2 x quad text--- (2)$$I = \int_0^\pi \frac{8(\pi - x) \, dx}{4\cos^2 x + \sin^2 x} \quad \text{--- (2)}$$
### Step 1: Eliminating the x$x$ term in numerator
Adding (1) and (2):
2I = 8pi int_0^pi fracdx4cos^2 x + sin^2 x$$2I = 8\pi \int_0^\pi \frac{dx}{4\cos^2 x + \sin^2 x}$$
I = 4pi int_0^pi fracdx4cos^2 x + sin^2 x$$I = 4\pi \int_0^\pi \frac{dx}{4\cos^2 x + \sin^2 x}$$
Since the integrand is symmetric about x = pi/2$x = \pi/2$:
I = 8pi int_0^pi/2 fracdx4cos^2 x + sin^2 x$$I = 8\pi \int_0^{\pi/2} \frac{dx}{4\cos^2 x + \sin^2 x}$$
### Step 2: Integration using sec^2 x$\sec^2 x$ substitution
Divide numerator and denominator by cos^2 x$\cos^2 x$:
I = 8pi int_0^pi/2 fracsec^2 x \, dx4 + tan^2 x$$I = 8\pi \int_0^{\pi/2} \frac{\sec^2 x \, dx}{4 + \tan^2 x}$$
Let t = tan x implies dt = sec^2 x \, dx$t = \tan x \implies dt = \sec^2 x \, dx$
At x = 0$x = 0$, t = 0$t = 0$; at x = pi/2$x = \pi/2$, t to infty$t \to \infty$.
I = 8pi int_0^infty fracdtt^2 + 2^2$$I = 8\pi \int_0^\infty \frac{dt}{t^2 + 2^2}$$
I = 8pi left[ frac12 tan^-1left(fract2right) right]_0^infty = 4pi left( fracpi2 - 0 right) = 2pi^2$$I = 8\pi \left[ \frac{1}{2} \tan^{-1}\left(\frac{t}{2}\right) \right]_0^\infty = 4\pi \left( \frac{pi}{2} - 0 \right) = 2\pi^2$$
### Pattern Recognition
The presence of a linear x$x$ factor in the numerator of a definite integral with symmetric trigonometric bounds is almost always eliminated using the a+b-x$a+b-x$ property. This reduces the integral to a standard substitution problem.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Mathematics: Integrals