$\cos\:\left(\frac{\pi\:}{4}-x\right)=\frac{1}{2}$

$-15y^6+20y^4-95xy^2+45xy^4105x^2$

$x\left(x-5\right)^3$

$\left(10x+3y-8\right)-\left(17x-40y+1\right)$

$\frac{6xy+3x^2y}{x^2-4}\cdot\frac{x^2-3x+2}{12xy}$

$\left(b+2a+n\right)^2$

$\left(a+b\right)\left(a-b\right)\left(a^2-y^3+6\right)$