$3a+\left\{b-2-\left[\left(a-b\right)+\left(b-1\right)\right]\right\}$

$ln\left(\frac{\left(1-x\right)}{1+2x}\right)$

$-4x^2+36x-51$

$\left(\frac{1}{2}x^2-\frac{2}{3}x\right)^2$

$2\left(\sin^2\left(x\right)\right)=-\sin\left(x\right)$

$-\left(-5\right)-\left(-1\right)$

$\frac{\cos^2\left(x\right)+4\cos\left(x\right)+5}{\cos\left(x\right)-1}$