Question

Sin^4x+sin^2x*cos^2x-1

Answer 1

$sin^4 x+sin^2 x*cos^2 x-1=sin^2 x*(sin^2x +cos^2 x)-1=sin^2 x*1-1=sin^2 x -1=-cos^2 x$

Answer 2

(sin^2х)^2+sin^2x*cos^2x-1=((sin^2х)^2+sin^2x*cos^2x)-1=
=sin^2х(sin^2х+cos^2x)-1=sin^2х-1 

(sin^2x)^2- это sin^4x