$$\cot^2\left(x\right)+\csc\left(x\right)-19$$

$$a^2+24x^2a^3+144x^4a^4$$

$$2x-27-12$$

$$\lim_{x\to1.9}\:\left(x^2-3x+1\right)$$

$$x\frac{dx}{dt}+4=0$$

$$27c^3\:-\:d^3\:$$

$$y\:+\:y'\:=\:e^x\:cosx$$