$\cos\left(\pi-x\right)=\cos\left(\pi+x\right)$

$4\left(\frac{x}{8}-2\right)=\frac{1}{4}\left(2x-20\right)$

$\frac{81x^4y^2}{2}+36x^2y+8$

$\left(6f-5a+5\right)-\left(5f-6+5af\right)$

$\left(3a-2\right)\left(7a-4\right)$

$30+29+28+27+26+25+25+25+24+23+22+22+21$

$cos2x=2+4sinx$