$x^6-4x^2$

$x^2+11=0$

$x\left(1+y^2\right)^{\frac{1}{2}}dy\:=\:y\left(1+x^2\right)^{\frac{1}{2}dx}$

$4a^2+28a+49$

$4-3\cdot\left[2\cdot\left(-7+4\right)-\left(2-5\right)\cdot3-1\right]$

$2x^{2}+25=75$

$\cot\left(x\right)+\tan\left(x\right)=\tan\left(x\right)\cdot\sin^2x^{-2}$