# How do you simplify the expression #cos^2A(sec^2A-1)#?

##### 1 Answer

Oct 1, 2016

with exclusion

#### Explanation:

Note that:

#sec A = 1/(cos A)#

#sin^2 A + cos^2 A = 1#

So we find:

#cos^2 A (sec^2 A - 1) = (cos^2 A)/(cos^2 A) - cos^2 A#

#color(white)(cos^2 A (sec^2 A - 1)) = 1 - cos^2 A#

#color(white)(cos^2 A (sec^2 A - 1)) = sin^2 A#

Note that this identity does not hold for