Answer:
Step-by-step explanation:
cos^2+sin^2 = 1 ( rule)
cos^4x-cos^2x simplify
- cos^2( -cos^2 +1 ) -cos^2 common
or -cos^2 ( 1-cos^2)
since cos^2 + sin^2 = 1
substitute : -cos^2 ( sin^2 )
substitute : -(1-sin^2 ) ( sin^2)
multiply : -sin^2 + sin^4 or sin^4 - sin^2
it is verified that sin^4 -sin^2= cos^4-cos^2
hope it helps
