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JEE Advanced 2022 · Limits and Derivatives

If β=lim⁡x→0ex3−(1−x3)13+((1−x2)12−1)sin⁡xxsin⁡2x\beta = \lim_{x \to 0} \frac{e^{x^{3}} - \left(1 - x^{3}\right)^{\frac{1}{3}} + \left(\left(1 - x^{2}\right)^{\frac{1}{2}} - 1\right)\sin x}{x \sin^{2} x}, then the value of 6β6\beta is ______.

Answer: 55

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If β = lim_(x → 0) (e^(x³) - (1 - x³)^(1/3) + ((1 - x²)^(1/2) - 1)sin x)/(x sin² x), then the value of 6β is ______. β=lim⁡x→0ex3−(1−x3)1/3+((1−x2)1/2−1)sin⁡xxsin⁡2x\beta = \lim_{x \to 0} \dfrac{e^{x^{3}} - (1 - x^{3})^{1/3} + \left((1 - x^{2})^{1/2} - 1\right)\sin x}{x \sin^{2} x} At x→0: numerator→0, denominator→0⇒00 form\text{At } x \to 0:\ \text{numerator} \to 0,\ \text{denominator} \to 0 \Rightarrow \dfrac{0}{0} \text{ form} Find β, then 6β\text{Find } \beta, \text{ then } 6\beta Plan: expand numerator & denominator in powers of x, keep leading terms\text{Plan: expand numerator \& denominator in powers of } x,\ \text{keep leading terms} sin⁡x=x−x36+⋯⇒sin⁡2x≈x2\sin x = x - \dfrac{x^3}{6} + \cdots \Rightarrow \sin^2 x \approx x^2 xsin⁡2x≈x⋅x2=x3x \sin^2 x \approx x \cdot x^2 = x^3 ex3=1+x3+x62+⋯e^{x^3} = 1 + x^3 + \dfrac{x^6}{2} + \cdots (1−x3)1/3=1−x33−x69+⋯(1 - x^3)^{1/3} = 1 - \dfrac{x^3}{3} - \dfrac{x^6}{9} + \cdots ex3−(1−x3)1/3=x3+x33+⋯=43x3+⋯e^{x^3} - (1 - x^3)^{1/3} = x^3 + \dfrac{x^3}{3} + \cdots = \dfrac{4}{3}x^3 + \cdots (1−x2)1/2−1=−x22+⋯ ,sin⁡x≈x(1 - x^2)^{1/2} - 1 = -\dfrac{x^2}{2} + \cdots, \qquad \sin x \approx x ((1−x2)1/2−1)sin⁡x=−x32+⋯\left((1 - x^2)^{1/2} - 1\right)\sin x = -\dfrac{x^3}{2} + \cdots num=43x3−12x3+⋯\text{num} = \dfrac{4}{3}x^3 - \dfrac{1}{2}x^3 + \cdots =(43−12)x3=56x3+⋯= \left(\dfrac{4}{3} - \dfrac{1}{2}\right)x^3 = \dfrac{5}{6}x^3 + \cdots β=lim⁡x→056x3+⋯x3+⋯=56\beta = \lim_{x \to 0} \dfrac{\tfrac{5}{6}x^3 + \cdots}{x^3 + \cdots} = \dfrac{5}{6} 6β=6⋅56=56\beta = 6 \cdot \dfrac{5}{6} = 5 6β=5\boxed{6\beta = 5} β=56,6β=5\beta = \dfrac{5}{6}, \qquad 6\beta = 5

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