Question

How do you find the value of $\cos \pi$?

Answer 1

Calculate the value of trigonometric ratio:

Let $y$ be the value of $\cos \pi$.

$\therefore y=\cos \mathrm{\pi }$

We know that $\mathbf{\pi }\mathbf{=}\mathbf{180}\mathbf{°}$

$\therefore y=\cos 180°$

$=\cos \left(180°-0°\right)$

$=-\cos 0°$ $\left[\because cos\left(180°-a°\right)=-cosa°\right]$

$=-1$ $\left[\because cos0°=1\right]$

Hence, the value of $\mathit{c}\mathit{o}\mathit{s}\mathit{\pi }$ is $\mathbf{-}\mathbf{1}$.