Question 427300
Expand the left side:


{{{(4sin^2(x) + 12sin(x)cos(x) + 9 cos^2(x)) + (9sin^2(x) - 12sin(x)cos(x) + 4cos^2(x))}}}


The {{{12 sin(x)cos(x)}}} terms cancel out, leaving


{{{4sin^2(x) + 9 cos^2(x) + 9sin^2(x) + 4cos^2(x)}}}


Collect like terms to obtain


{{{13sin^2(x) + 13cos^2(x) = 13(sin^2(x) + cos^2(x))}}}. Since {{{sin^2(x) + cos^2(x) = 1}}} we conclude that the entire expression is equal to 13.