$6+a=15$

$\int\frac{\left(x+1\right)}{\left(x^2+1\right)^2}dx$

$4cos\:^2\left(x\right)-tan\:^2\left(x\right)-1$

$\left(\left(\sqrt[3]{x-5}\right)-\left(\sqrt[3]{4-4x}\right)\right)\frac{1}{\left(x^3+27\right)}$

$1-\sin^2x=\frac{1}{\csc^2\left(x\right)}$

$\left(1+\sin z\right)\left(1+\sin z\right)=\frac{1}{\sec^2z}$

$4a\left(-6b+8z\right)$