Q11 / 46 · NTA Abhyas (JEE Main) 2020 · Mathematics · Differentiation

If y=acos⁡(log⁡x)+bsin⁡(log⁡x), where a & b are parameters, then x2y"+xy'is equal to

  • A
    y
  • Correct answer
    B
    -y
  • C
    2y
  • D
    -2y

Solution

y=acos⁡(log⁡x)+bsin⁡(log⁡x)

On differentiating w.r.t. x, we get

y ′ = −asin(logx) x + bcos(logx) x

⇒x y ′ =−asin(logx)+bcos(logx)

Again, on differentiating w.r.t. x, we get

x y ″ + y ′ =−acos(logx) 1 x −bsin(logx) 1 x

⇒ x 2 y ″ + y ′ x=− acos(logx)+bsin(logx ]

⇒ x 2 y ″ +x y ′ =−y

Hence, the correct answer is option: 'B'.

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