$sin\left(a+b\right)+cos\left(a+b\right)$

$-0^3+3\left(0\right)^2+7\left(0\right)$

$2ax^4-20x^3+8a^4x^7$

$36y^2\:-\:12xy\:+\:x^2$

$\frac{2}{3}\left(x-5\right)\frac{1}{2}x=-3$

$\lim_{x\to25}\left(\frac{\sqrt[3]{25}-\sqrt[3]{x}}{\sqrt{x}-5}\right)$