$7\left(-5\right)^2+21\left(-5\right)-28$

$x^4-32x^2+256$

$\frac{d}{dx}\left(sin\left(x\right)=sin\left(y\right)\right)$

$2x+3x+5+6+4y+2y$

$\int_0^{\infty}\left(5e^{-x}\right)dx$

$\lim_{x\to\frac{\pi}{2}}\left(\frac{tanx}{arctan\left(cosx\right)}\right)$

$\tan a=137$