$-7n^3.\:-7n$

$\cot x\left(1-\cos x\right)=\sin x$

$\frac{3}{4}\sin\left(x\right)-\frac{1}{4}\sin\left(3x\right)=\sin^3\left(x\right)$

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

$\frac{2}{5}x^2\frac{3}{8}y^2+\frac{1}{10}x^2-\frac{1}{2}y^2$

$x^2-26x+169=-13$

$6\left(6.75\right)$