$$4.5\cdot\tan\left(54.6\right)$$

$$x\left(y^2+1\right)dx+\left(x^2+1\right)dy=0$$

$$100\frac{dy}{dx}+\frac{1}{100}=12$$

$$35+x-6x^2$$

$$18sin\left(x\right)-18sin\left(x\right)cos\left(x\right)=\frac{36}{\pi}$$

$$-9\:+4\:\cdot\:-27$$

$$x^2-x-156$$