Question 947382
cos^4 theta - sin^4 theta = cos^2 theta - sin^2 theta
simplify:
{{{cos^4(x)-sin^4(x)=cos^2(x)-sin^2(x)}}}
{{{(cos^2(x)+sin^2(x))(cos^2(x)-sin^2(x))=cos^2(x)-sin^2(x)}}}
{{{cos^2(x)+sin^2(x)=1}}}