For alpha, beta, gamma in mathbbR, if lim_x to 0 fracx^2 sin alpha x + (gamma - 1) e^x^2sin 2x - beta x = 3, then beta + gamma - alpha is equal to:

Solution & Explanation

### Related Formula Standard Taylor series expansions centered at x=0: sin x = x - fracx^36 + dots e^x = 1 + x + fracx^22 + dots ### Core Logic Since the limit evaluates to a finite value (3) while the denominator goes to zero when x to 0 (if 2-beta=0), the numerator coefficients of lower-degree terms must vanish to resolve the indetermination. ### Step 1: Substitute Expansions Substitute series expansions into numerator and denominator: textNumerator = x^2(alpha x) + (gamma - 1)left(1 + x^2 + fracx^42 + dotsright) textDenominator = left(2x - frac8x^36 + dotsright) - beta x = (2 - beta)x - frac43x^3 + dots ### Step 2: Equate Coefficients to Avoid Infinity Combine terms by degree: lim_x to 0 frac(gamma - 1) + (gamma - 1)x^2 + alpha x^3(2 - beta)x - frac43x^3 = 3 For a valid finite limit, the lowest power in the numerator cannot be smaller than the lowest power in the denominator. * Constraining constant term to zero: gamma - 1 = 0 implies gamma = 1 * This also forces the x^2 coefficient to vanish: (gamma - 1) = 0. * To balance the remaining leading x^3 terms, the x term in the denominator must vanish: 2 - beta = 0 implies beta = 2. ### Step 3: Evaluate Remaining Limit Value Now compute the remaining simplified limit of x^3 variables: lim_x to 0 fracalpha x^3-frac43x^3 = frac-3alpha4 = 3 implies alpha = -4 ### Step 4: Final Expression Calculation Substitute the found parameters into beta + gamma - alpha: beta + gamma - alpha = 2 + 1 - (-4) = 7 ### Pattern Recognition Taylor expansions are far safer than consecutive L'Hopital iterations here because multiple variables are spread across distinct polynomial powers, isolating components explicitly by structural degree. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Limits, Continuity and Differentiability

More Limits, Continuity and Differentiability Previous-Year Questions — Page 6

Q15 jee_main_2024_01_february_morning Continuity and Differentiability of Piecewise Functions
Let f:Rrightarrow R be defined as f(x)=begincasesfraca-b cos 2xx^2 & , & x<0\\ x^2+cx+2 & , & 0le xle1\\ 2x+1 & , & x>1endcases If f is continuous everywhere in R and m is the number of points where f is NOT differentiable, then m+a+b+c equals:
  • A. 1
  • B. 4
  • C. 3
  • D. 2

Solution

### Related Formula For a function to be continuous at a boundary point x = x_0, the left-hand limit, right-hand limit, and exact function value must all match: lim_x to x_0^- f(x) = lim_x to x_0^+ f(x) = f(x_0) ### Core Logic Let's enforce continuity at the critical boundaries, x = 1 and x = 0: 1. **Continuity at x = 1:** f(1^-) = f(1) = 1^2 + c(1) + 2 = 3 + c f(1^+) = 2(1) + 1 = 3 Equating both configurations: 3 + c = 3 implies c = 0. 2. **Continuity at x = 0:** f(0^+) = f(0) = 0^2 + 0 + 2 = 2 f(0^-) = lim_h to 0 fraca - b cos(2h)h^2 Using the Taylor expansion cos(2h) = 1 - frac4h^22! + frac16h^44! - dots = 1 - 2h^2 + frac23h^4 - dots lim_h to 0 fraca - bleft(1 - 2h^2 + frac23h^4 - dotsright)h^2 = lim_h to 0 frac(a-b) + 2bh^2 - frac23bh^4 + dotsh^2 For the limit to exist and remain finite, the constant term must vanish: a - b = 0 implies a = b. The value of the limit is then equal to 2b. To satisfy continuity: 2b = 2 implies b = 1 implies a = 1. ### Step 1: Checking Differentiability at x = 0 Evaluating the Left-Hand Derivative (LHD) at x = 0 using values a=1, b=1: textLHD = lim_h to 0 fracf(-h) - f(0)-h = lim_h to 0 fracfrac1 - cos(2h)h^2 - 2-h textLHD = lim_h to 0 fracleft(2 - frac23h^2 + dotsright) - 2-h = lim_h to 0 frac23h = 0 Evaluating the Right-Hand Derivative (RHD) at x = 0: textRHD = lim_h to 0 fracf(h) - f(0)h = lim_h to 0 frac(h^2 + 2) - 2h = lim_h to 0 h = 0 Since textLHD = textRHD = 0, the function is fully differentiable at x = 0. ### Step 2: Checking Differentiability at x = 1 Evaluating derivatives at x = 1 with parameter c = 0: - For 0 le x le 1, f(x) = x^2 + 2 implies f'(x) = 2x implies f'(1^-) = 2. - For x > 1, f(x) = 2x + 1 implies f'(x) = 2 implies f'(1^+) = 2. Since the left derivative equals the right derivative at x = 1, the function is differentiable at x = 1. Thus, the function is differentiable everywhere, giving m = 0 points of non-differentiability. ### Step 3: Finding the Requested Evaluation Sum Now substitute the values m=0, a=1, b=1, c=0 into the target equation: m + a + b + c = 0 + 1 + 1 + 0 = 2 ### Pattern Recognition Sees: Continuity conditions paired with rational surd trigonometric expansion. Shortcut: When tracking indeterminate limits like fraca-bcos 2xx^2, matching expansions row by row prevents typical computation errors encountered with standard L'Hopital differentiation loops. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Limits, Continuity and Differentiability
Q25 jee_main_2024_01_february_morning One Sided Limits
Let {x} denote the fractional part of x and f(x)=fraccos^-1(1-\x\^2)sin^-1(1-\x\)\x\-\x\^3, xne0. If L and R respectively denotes the left hand limit and the right hand limit of f(x) at x=0 then frac32pi^2(L^2+R^2) is equal to
Numerical Answer. Answer: 18 to 18

Solution

### Related Formula Definition of fractional part function: - For x to 0^+, \x\ = x - 0 = x. - For x to 0^-, \x\ = x - (-1) = x + 1. ### Core Logic Let's evaluate the left-hand limit (L) and right-hand limit (R) separately by setting up substitution parameters around the point x=0. ### Step 1: Evaluate Right Hand Limit (R) As x to 0^+, substitute \x\ = h where h to 0: R = lim_h to 0 fraccos^-1(1-h^2)sin^-1(1-h)h(1-h^2) = lim_h to 0 fraccos^-1(1-h^2)h cdot left(fracsin^-111right) = fracpi2 lim_h to 0 fraccos^-1(1-h^2)h Let cos^-1(1-h^2) = theta implies 1-h^2 = costheta implies h^2 = 1 - costheta = 2sin^2(theta/2). As h to 0, theta to 0, so h approx fracthetasqrt2: R = fracpi2 lim_theta to 0 fracthetafracthetasqrt2 = fracpisqrt2 ### Step 2: Evaluate Left Hand Limit (L) As x to 0^-, let x = -h implies \x\ = 1-h where h to 0: L = lim_h to 0 fraccos^-1(1-(1-h)^2)sin^-1(1-(1-h))(1-h) - (1-h)^3 L = lim_h to 0 fraccos^-1(2h-h^2)sin^-1h(1-h)[1 - (1-h)^2] = lim_h to 0 fraccos^-1(0)sin^-1h1 cdot (2h-h^2) L = fracpi2 lim_h to 0 left( fracsin^-1hh cdot frac12-h right) = fracpi2 cdot 1 cdot frac12 = fracpi4 ### Step 3: Calculate the Target Value Substituting the computed limits L = fracpi4 and R = fracpisqrt2 into the target expression: frac32pi^2(L^2+R^2) = frac32pi^2 left( fracpi^216 + fracpi^22 right) = 32 left( frac116 + frac12 right) = 2 + 16 = 18 ### Pattern Recognition Sees: Discontinuous fractional part function framing an indeterminate limit form. Trap: Be extremely careful when managing fractional limits below zero: \x\ to 1 when x to 0^-, transforming expressions significantly compared to right-hand approaches. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Limits, Continuity and Differentiability Class 11 Mathematics: Relations and Functions
Q17 jee_main_2024_29_january_evening Higher Order Derivatives
Let y = log_eleft(frac1 - x^21 + x^2 ight), -1 < x < 1. Then at x = frac12, the value of 225(y' - y'') is equal to
  • A. 732
  • B. 746
  • C. 742
  • D. 736

Solution

### Related Formula y = ln(1 - x^2) - ln(1 + x^2) ### Core Logic Let us differentiate the simplified logarithm form: y' = frac-2x1 - x^2 - frac2x1 + x^2 = -2x left( frac1 + x^2 + 1 - x^21 - x^4 right) = frac-4x1 - x^4 Now, computing the second derivative y'' using the quotient rule: y'' = frac-4(1 - x^4) - (-4x)(-4x^3)(1 - x^4)^2 = frac-4 + 4x^4 - 16x^4(1 - x^4)^2 = frac-4(1 + 3x^4)(1 - x^4)^2 ### Step 1: Finding the Combined Value Let us substitute x = frac12 into the expressions: 1 - x^4 = 1 - frac116 = frac1516 y' = frac-4(1/2)15/16 = frac-215/16 = -frac3215 y'' = frac-4(1 + 3/16)(15/16)^2 = frac-4(19/16)225/256 = -frac194 times frac256225 = -frac19 times 64225 = -frac1216225 ### Step 2: Resolving the Target Multiplier Compute y' - y'': y' - y'' = -frac3215 - left(-frac1216225right) = -frac480225 + frac1216225 = frac736225 Multiplying this by 225: 225(y' - y'') = 225 times frac736225 = 736 ### Pattern Recognition Always break log quotient blocks into independent terms before differentiating (lnfracab = ln a - ln b). Differentiating fractions directly invites errors. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Continuity and Differentiability
Q30 jee_main_2024_29_january_evening Leibniz Rule and Limits
Let the slope of the line 45x + 5y + 3 = 0 be 27r_1 + frac9r_22 for some r_1, r_2 in mathbbR. Then lim_x rightarrow 3 left(int_3^x frac8t^2frac3r_2 x2 - r_2 x^2 - r_1 x^3 - 3x\, dtright) is equal to
Numerical Answer. Answer: 12 to 12

Solution

### Related Formula Using the Newton-Leibniz formula for differentiating an integral: fracddx left( int_a^x f(t)\, dt right) = f(x) ### Core Logic The line equation is 45x + 5y + 3 = 0 implies y = -9x - frac35. Its slope is -9. Equating the slope expressions: 27r_1 + frac9r_22 = -9 implies 3r_1 + fracr_22 = -1 quad dots (i) ### Step 1: Applying L'Hopital's Rule to the Limit The limit is in the frac00 form as x rightarrow 3. Differentiating the numerator and denominator using L'Hopital's Rule: textLimit = lim_x rightarrow 3 frac8x^2frac3r_22 - 2r_2 x - 3r_1 x^2 - 3 ### Step 2: Evaluating the Target Denominator Value Substitute x = 3 into the differentiated structure: textDenominator = frac3r_22 - 6r_2 - 27r_1 - 3 = -frac9r_22 - 27r_1 - 3 = -9left(3r_1 + fracr_22right) - 3 From equation (i), we substitute 3r_1 + fracr_22 = -1: textDenominator = -9(-1) - 3 = 9 - 3 = 6 Evaluating the full limit: textLimit = frac8(3)^26 = frac726 = 12 ### Pattern Recognition L'Hopital transformations reduce parameter sets back into exact multiples of the initial constraint formula. This avoids solving for r_1 and r_2 individually. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Mathematics: Limits, Continuity and Differentiability
Q13 jee_main_2024_27_jan_morning Continuity at a Point
Consider the function: f(x) = begincases fraca(7x-12-x^2)b(x^2-7x+12) & , x < 3 \\ frac2sin(x-3)x-[x] & , x > 3 \\ b & , x = 3 endcases Where [x] denotes the greatest integer less than or equal to x. If S denotes the set of all ordered pairs (a, b) such that f(x) is continuous at x=3 then the number of elements in S is:
  • A. 2
  • B. textInfinitely many
  • C. 4
  • D. 1

Solution

### Related Formula textFor continuity at x=a, lim_x to a^- f(x) = lim_x to a^+ f(x) = f(a) lim_h to 0 fracsin hh = 1 ### Core Logic We need to evaluate the Left Hand Limit (LHL) and Right Hand Limit (RHL) at x = 3. For LHL (x < 3): f(x) = fraca(7x-12-x^2)b(x^2-7x+12) Factor the polynomials: Numerator quadratic: -(x^2 - 7x + 12) f(x) = frac-a(x^2-7x+12)b(x^2-7x+12) = frac-ab Thus, lim_x to 3^- f(x) = frac-ab. ### Step 1: Evaluating Right Hand Limit For RHL (x > 3), as x to 3^+, the value of the greatest integer function [x] = 3. f(x) = frac2sin(x-3)x-[x] Substituting [x] = 3: lim_x to 3^+ f(x) = lim_x to 3^+ frac2sin(x-3)x-3 Applying the standard limit lim_theta to 0 fracsin thetatheta = 1: textRHL = 2(1) = 2 ### Step 2: Equating Limits For the function to be continuous at x=3, LHL = RHL = f(3). We are given f(3) = b. Therefore: frac-ab = 2 = b From the right equation, b = 2. Substitute b into the left equation: frac-a2 = 2 Rightarrow a = -4 ### Step 3: Final Conclusion The only ordered pair (a, b) that makes the function continuous is (-4, 2). The number of elements in the set S is 1. ### Pattern Recognition For limits involving [x] as x to k^+, you can immediately replace [x] with k. When evaluating algebraic limits where the numerator is the exact negative of the denominator, they cancel out natively leaving just the constant ratio. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Maths: Continuity and Differentiability Class 11 Maths: Limits and Derivatives
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