$2x+7y-3x+y-x^2$

$xy'\:=\:x\:sin\:\left(x-y\right)$

$6xy-3x^2$

$\lim_{x\to-1}\frac{x^{2\:}-1}{\sqrt{x-1}}$

$\frac{\frac{1}{\csc\left(x\right)}}{\cos\left(x\right)-\frac{1}{\sec\left(x\right)^3}}=\frac{1}{sinxcosx}$

$\frac{m^2-36}{m+6}$

$\left(b^2+\frac{1}{2}\right)\left(b^2-\frac{1}{2}\right)$