Question

sin^4a+sin^2a*cos^2a

Answer 1

sin^4(a) + sin^2(a)*cos^2(a) = sin^2(a)*( sin^2(a) + cos^2(a) ) =
= [ осн. триг. тождество sin^2(a)+cos^2(a) = 1, поэтому ...] =
= sin^2(a).