JEE PYQ: Differentiation Question 5
Question 5 - 2020 (03 Sep Shift 1)
If $y^2 + \log_e(\cos^2 x) = y$, $x \in \left(-\frac{\pi}{2}, \frac{\pi}{2}\right)$, then:
(1) $y’’(0) = 0$ (2) $|y’(0)| + |y’’(0)| = 1$ (3) $|y’’(0)| = 2$ (4) $|y’(0)| + |y’’(0)| = 3$
Show Answer
Answer: (3) $|y’’(0)| = 2$
Solution
Differentiating: $2yy’ - 2\tan x = y’$. At $x = 0$: $y’(0) = 0$. Differentiating again and putting $x = 0$: $y’’(0) = 2$.