$$\left(4x-a^2\right)^2$$

$$x^2-42x$$

$$\left(9m+8\right)+\left(2m-1\right)$$

$$4-2x^2=0$$

$$\left(\frac{3}{5}a+\:\frac{2}{7}b+\:\frac{6}{5c}\right)^2$$

$$-\sec\left(x\right)^2+\csc\left(x\right)^2=\sec\left(x\right)^2.\csc\left(x\right)^2$$

$$64\:-\:4\:0\:+\:4$$