If $y=2^{a x}$ and $\left(\frac{d y}{d x}\right)_{x=1}=\log 256$, then $a=$

If $y=2^{a x}$ and $\left(\frac{d y}{d x}\right)_{x=1}=\log 256$, then $a=$
  1. 4
  2. 2
  3. 8
  4. 3

Solution

$y=2^{2 x} \Rightarrow \frac{d y}{d x}=2^{2 x}(\log 2)(a)$ $\therefore\left(\frac{d y}{d x}\right)_{x=1}=\left(2^{a}\right)(a)(\log 2)$ As per condition given $\left(2^{a}\right)(a)(\log 2)=\log 256=\log (2)^{8}=8 \log 2$ $\therefore\left(2^{a}\right)(a)=8 \Rightarrow a=2$

Asked in: MHT CET 2020 (20 Oct Shift 2)

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