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 9

Q17 jee_main_2024_31_jan_morning Continuity Check
Let g(x) be a linear function and f(x) = begincases g(x) & , x le 0 \\ left(frac1+x2+xright)^frac1x & , x > 0 endcases is continuous at x = 0. If f'(1) = f(-1), then the value of g(3) is
  • A. frac13 log_e left(frac49e^1/3right)
  • B. frac13 log_e left(frac49right) + 1
  • C. log_e left(frac49right) - 1
  • D. log_e left(frac49e^1/3right)

Solution

### Core Logic Let g(x) = ax + b. Since f(x) is continuous at x = 0: lim_x to 0^+ f(x) = f(0) lim_x to 0 left(frac1+x2+xright)^frac1x = b As x to 0, the base approaches frac12, and exponent approaches infty. Thus, left(frac12right)^infty = 0. So, b = 0. Thus, g(x) = ax. ### Step 1: Calculate Derivative For x > 0, f(x) = left(frac1+x2+xright)^frac1x. Let y = f(x). ln y = frac1x lnleft(frac1+x2+xright) Differentiating both sides w.r.t x: frac1y y' = -frac1x^2 lnleft(frac1+x2+xright) + frac1x cdot frac2+x1+x cdot frac1(2+x) - (1+x)1(2+x)^2 y' = y left[ -frac1x^2 lnleft(frac1+x2+xright) + frac1x(1+x)(2+x) right] ### Step 2: Apply Condition At x=1, y = f(1) = frac23. f'(1) = frac23 left[ -1 lnleft(frac23right) + frac16 right] = -frac23 lnleft(frac23right) + frac19 Also f(-1) = g(-1) = -a. Given f'(1) = f(-1) implies -a = -frac23 lnleft(frac23right) + frac19. a = frac23 lnleft(frac23right) - frac19 ### Step 3: Evaluate g(3) g(3) = 3a = 2 lnleft(frac23right) - frac13 g(3) = lnleft(frac49right) - frac13 = lnleft(frac49right) - ln(e^1/3) = lnleft(frac49e^1/3right) ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Maths: Continuity and Differentiability Class 12 Maths: Application of Derivatives
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