JEE Main 2017 · 9 April · Online · Mathematics · Differentiation
B. −24- 24−24
Given y15+y−15=2x{y}^{\dfrac{1}{5}} + {y}^{- \dfrac{1}{5}} = 2xy51+y−51=2x⇒(15y−45−15y−65)dydx=2⇒ \left(\dfrac{1}{5}{y}^{- \dfrac{4}{5}} - \dfrac{1}{5}{y}^{- \dfrac{6}{5}}\right)\dfrac{dy}{dx} = 2⇒51y−54−51y−56dxdy=2⇒y′(y15−y−15)=10y⇒ {y}^{′}\left({y}^{\dfrac{1}{5}} - {y}^{- \dfrac{1}{5}}\right) = 10y⇒y′y51−y−51=10y⇒y′(2x2−1)=10y⇒ {y}^{′}\left(2\sqrt{{x}^{2} - 1}\right) = 10y⇒y′(2x2−1)=10y
⇒y′x2−1=5y⇒ {y}^{′}\sqrt{{x}^{2} - 1} = 5y⇒y′x2−1=5yDifferentiating againy′′(2x2−1)+y′22x2x2−1=10y′{y}^{′′}\left(2\sqrt{{x}^{2} - 1}\right) + {y}^{′}2\dfrac{2x}{2\sqrt{{x}^{2} - 1}} =10y'y′′(2x2−1)+y′22x2−12x=10y′⇒y′′(x2−1)+xy′=5x2−1(y′)⇒ {y}^{′′}\left({x}^{2} - 1\right) + x{y}^{′} = 5\sqrt{{x}^{2} - 1}\left({y}^{′}\right)⇒y′′(x2−1)+xy′=5x2−1(y′)⇒y′′(x2−1)+xy′−25y=0⇒ {y}^{′′}\left({x}^{2} - 1\right) + x{y}^{′} - 25y = 0⇒y′′(x2−1)+xy′−25y=0⇒λ=1,k=−25⇒ \lambda = 1, k = - 25⇒λ=1,k=−25