$\frac{\cos\left(x\right)^2}{1+\sin\left(x\right)^2}+\sin\left(x\right)^2$

$\left(\sin\left(x\right)+\cos\left(x\right)\right)\left(1-\frac{1}{2}\sin\left(2x\right)\right)$

$sec^2a-cos^2a$

$\frac{2n}{4n^2+1}x^{2n}$

$81x^2+72x+16=0$

$\left(x+1\right)\left(x+3\right)+\left(x-2\right)^2$

$sin\left(a+x\right)$