Question

Verify the identity. cot(x - pi/2) = -tan(x)

Answer 1

Answer:

See below.

Step-by-step explanation:

$\cot(x-\frac{\pi}{2})=-\tan(x)$

Convert the cotangent to cosine over sine:

$\frac{\cos(x-\frac{\pi}{2} )}{\sin(x-\frac{\pi}{2})} =-\tan(x)$

Use the cofunction identities. The cofunction identities are:

$\sin(x)=\cos(\frac{\pi}{2}-x)\\\cos(x)=\sin(\frac{\pi}{2}-x)$

To convert this, factor out a negative one from the cosine and sine.

$\frac{\cos(-(\frac{\pi}{2}-x ))}{\sin(-(\frac{\pi}{2}-x))} =-\tan(x)$

Recall that since cosine is an even function, we can remove the negative. Since sine is an odd function, we can move the negative outside:

$\frac{\cos((\frac{\pi}{2}-x ))}{-\sin((\frac{\pi}{2}-x))} =-\tan(x)\\-\frac{\sin(x)}{\cos(x)} =-\tan(x)\\-\tan(x)\stackrel{\checkmark}{=}-\tan(x)$