Answer
1
Work Step by Step
We can find the sine of coterminal angle that lies between $0^{\circ}$ and $360^{\circ}$ for convenience.
$\sin(-270^{\circ})= \sin(-270^{\circ}+360^{\circ})=\sin 90^{\circ}$
The terminal side of $90^{\circ}$ angle passes through (0,1). So $x=0,y=1$ and $r=1$.
$\sin 90^{\circ}=\frac{y}{r}=\frac{1}{1}=1$
