Question

Find the value of $\cos {270^o}$

Answer 1

Note that, since $270^\circ$ is greater than $90^\circ$, it is located in the third quadrant.
Alternatively, draw the graph for y = cosx and find y when $x = 270^\circ$

Complete step-by-step answer:
We know $270^\circ$is greater than $90^\circ$and is located in the third quadrant.
Therefore,
$\cos {270^o}$
$= \cos \left( {\dfrac{{3\pi }}{2}} \right)$
= 0
Therefore $\cos {270^o}$=0

Note:

Also, from the graph of $y{\text{ }} = {\text{ }}cosx$
we can see, cosine of the angles that are odd multiples of $\dfrac{\pi }{2}$ , is always zero.
Therefore $\cos {270^o}$= 0