$\left(x^2+4\right)\left(x^2-9\right)$

$-\sqrt{-9}$

$\left(9w+5x\right)\left(9w-5x\right)$

$729m^{12}-b^{15}$

$5-x-x-\left\{x-\left\{-\left[2x+\left(x-\left(x-1\right)\left(3-x\right)\right)\right]\right\}\right\}$

$4-\left(-12:4+\left(4-\left(4:-2+12-2\right)-6\right)\right)$

$-10+6+2$