Related Formula
∫ xⁿ dx = xⁿ⁺¹n+1 + c$$\int x^n dx = \frac{x^{n+1}}{n+1} + c$$
For integrals containing linear terms multiplied by the root of a quadratic, use the standard substitution L = (1)/(t)$L = \frac{1}{t}$.
Core Logic
Let 4x + 6 = (1)/(t) x = (1/t - 6)/(4)$4x + 6 = \frac{1}{t} \implies x = \frac{1/t - 6}{4}$.
Differentiating, 4 dx = -(1)/(t²) dt dx = -(dt)/(4t²)$4 dx = -\frac{1}{t^2} dt \implies dx = -\frac{dt}{4t^2}$.
We also need to map the quadratic part 4x² + 8x + 3 = 4(x² + 2x + 1) - 1 = 4(x+1)² - 1$4x^2 + 8x + 3 = 4\left(x^2 + 2x + 1\right) - 1 = 4(x+1)^2 - 1$.
Substitute x+1 = (1/t - 6)/(4) + 1 = (1/t - 2)/(4)$x+1 = \frac{1/t - 6}{4} + 1 = \frac{1/t - 2}{4}$:
4(x+1)² - 1 = 4((1/t - 2)/(4))² - 1 = ((1-2t)²)/(4t²) - 1$$4(x+1)^2 - 1 = 4\left(\frac{1/t - 2}{4}\right)^2 - 1 = \frac{(1-2t)^2}{4t^2} - 1$$
The integral becomes:
I(x) = ∫ 3 (-(dt)/(4t²))((1)/(t))√(((1-2t)²)/(4t²) - 1)$$I(x) = \int \frac{3 \left(-\frac{dt}{4t^2}\right)}{\left(\frac{1}{t}\right)\sqrt{\frac{(1-2t)^2}{4t^2} - 1}}$$
Step 1: Simplify Integral
I(x) = -(3)/(4) ∫ dtt √((1 - 4t + 4t² - 4t²)/(4t²))$$I(x) = -\frac{3}{4} \int \frac{dt}{t \sqrt{\frac{1 - 4t + 4t^2 - 4t^2}{4t^2}}}$$
I(x) = -(3)/(4) ∫ dtt √(1-4t)2t$$I(x) = -\frac{3}{4} \int \frac{dt}{t \frac{\sqrt{1-4t}}{2t}}$$
I(x) = -(3)/(2) ∫ dt√(1-4t)$$I(x) = -\frac{3}{2} \int \frac{dt}{\sqrt{1-4t}}$$
I(x) = -(3)/(2) (1-4t)1/2(1/2)(-4) + C = (3)/(4) √(1-4t) + C$$I(x) = -\frac{3}{2} \frac{(1-4t)^{1/2}}{(1/2)(-4)} + C = \frac{3}{4} \sqrt{1-4t} + C$$
Substituting back t = (1)/(4x+6)$t = \frac{1}{4x+6}$:
I(x) = (3)/(4) √(1 - (4)/(4x+6)) + C = (3)/(4) √((4x+2)/(4x+6)) + C$$I(x) = \frac{3}{4} \sqrt{1 - \frac{4}{4x+6}} + C = \frac{3}{4} \sqrt{\frac{4x+2}{4x+6}} + C$$
Step 2: Final Calculation
Given I(0) = √(3)4 + 20$I(0) = \frac{\sqrt{3}}{4} + 20$:
I(0) = (3)/(4)√((2)/(6)) + C = (3)/(4) 1√(3) + C = √(3)4 + C$$I(0) = \frac{3}{4}\sqrt{\frac{2}{6}} + C = \frac{3}{4}\frac{1}{\sqrt{3}} + C = \frac{\sqrt{3}}{4} + C$$
Thus, C = 20$C = 20$.
Now, evaluate I(1/2)$I(1/2)$:
I((1)/(2)) = (3)/(4)√((4(1/2)+2)/(4(1/2)+6)) + 20 = (3)/(4)√((4)/(8)) + 20 = (3)/(4) 1√(2) + 20 = 3√(2)8 + 20$$I\left(\frac{1}{2}\right) = \frac{3}{4}\sqrt{\frac{4(1/2)+2}{4(1/2)+6}} + 20 = \frac{3}{4}\sqrt{\frac{4}{8}} + 20 = \frac{3}{4}\frac{1}{\sqrt{2}} + 20 = \frac{3\sqrt{2}}{8} + 20$$
Comparing with a√(2)b + c$\frac{a\sqrt{2}}{b} + c$, we get a=3, b=8, c=20$a=3, b=8, c=20$.
(3,8) = 1$\gcd(3,8) = 1$, condition is met.
a + b + c = 3 + 8 + 20 = 31$$a + b + c = 3 + 8 + 20 = 31$$
Pattern Recognition
The integral format ∫ dx(ax+b)√(px²+qx+r)$\int \frac{dx}{(ax+b)\sqrt{px^2+qx+r}}$ classically demands substituting the linear outer piece as ax+b = 1/t$ax+b = 1/t$.
Chapter Mix
Class 12 Maths: Indefinite Integration