$\cos^4b-\sin^4b=\cos2b$

$-7x-2y-\left(-11x+8y\right)-\left(\left(3x+5y\right)-\left(9x-2y\right)\right)$

$6x^5y^3z+18x^3y^4z^5-21x^4y^2z^4$

$\frac{2}{3}\sec\left(\frac{x}{3}\right)$

$\lim_{x\to4}\left(\frac{\left|x-4\right|}{x-4}\right)$

$4tan\left(x\right)+8=0$

$\left(3x^4+5y^2\right)^2$