Question 870190
{{{sin^4 (x) - cos^4 (x) = 1 - 2cos^2 (x )}}}


{{{(sin^2(x)+cos^2(x))*(sin^2(x)-cos^2(x))}}}

{{{(1)(1-cos^2(x)-cos^2(x))}}}

{{{1-2cos^2(x)}}}