$4.12-2$

$\frac{cos\left(x\right)sec\left(x\right)}{cot\left(x\right)}$

$16y^2-56+3$

$\frac{\cos\left(x-y\right)-\cos\left(x\right)\cdot\cos\left(y\right)}{\cos\left(x\right)\cdot\sin\left(y\right)}$

$9a^2-8a+a^2+3a$

$\left(5a-7\right)x\left(5a+7\right)$

$\frac{\:2x^4-5x^3+7x^2-3x+1}{x+1}$