$\left(x-10\right)^2-\left(8x-1\right)^2$

$\frac{\sin\left(6x\right)}{\sin\left(3x\right)}-\frac{\cos\left(6x\right)}{\cos\left(3x\right)}=\sec\left(3x\right)$

$4cos2x+3cosx$

$\int\frac{3x}{x^2+2x-8}dx$

$\frac{dx}{dt}+\frac{1}{3}x=\cos\left(2t\right)$

$\frac{a^2+2a+3}{a+3}$

$2\left(2x+5\right)+2\left(3x+1\right)$