Question

If a normal to the curve $y=f\left(x\right)$ at a point makes ${135}^{\circ }$ angle with $x$ - axis then at that point $\frac{dy}{dx}$ equals-

• A. $1$
• B. $-1$
• C. $0$
• D. $\infty$

Answer 1

The correct option is A $1$

Given, $\frac{dx}{dy}=\tan {135}^0=-1=m$(say)
$\Rightarrow \frac{dy}{dx}=-\frac{1}{m}=1$
Hence, option 'A' is correct.