Write cot(x) in terms of cos(x). You may assume x is in quadrant I.

Can you show $\sin(x)=\cos\left(x-\frac{\pi}{2}\right)~?$
If so, then $\cot(x)=\dfrac {\cos(x)}{\sin(x)}=~?$
Also $\displaystyle sin(x) =\sqrt{1 - (cos(x))^2}$ since x is in first quadrant.