How do you verify the identity (cos^2theta-sin^2theta)=(cottheta-tantheta)/(tantheta+cottheta)?

1 Answer
Sep 2, 2016

See explanation...

Explanation:

Use:

sin^2 theta + cos^2 theta = 1

tan theta = sin theta / cos theta

cot theta = cos theta / sin theta

Hence:

cos^2 theta - sin^2 theta = (cos^2 theta - sin^2 theta)/(sin^2 theta + cos^2 theta)

color(white)(cos^2 theta - sin^2 theta) = ((cos^2 theta - sin^2 theta) -: (cos theta sin theta))/((sin^2 theta + cos^2 theta) -: (cos theta sin theta))

color(white)(cos^2 theta - sin^2 theta) = (cos theta / sin theta - sin theta / cos theta)/(sin theta/cos theta + cos theta/sin theta)

color(white)(cos^2 theta - sin^2 theta) = (cot theta - tan theta)/(tan theta + cot theta)