$$\left(1-2cos^2x+cos^4x\right)^2$$

$$\cos^2x\sin x\frac{dy}{dx}+\left(\cos^3x\right)y=1$$

$$\sqrt{-49}\cdot\sqrt{-81}$$

$$t^4+31=20$$

$$30x^2+7x+15$$

$$2\left(\log\left(x+2\right)+2.5\left(\log\left(x+5\right)\right)\right)$$

$$\frac{1}{36}\cdot\left(2187a+686b\right)$$