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

$$\left(y^2\:+\:3\:x\:y\right)\:\:dx\:=\:\left(4\:x^2\:+\:x\:y\right)\:\:dy$$

$$\left(+20\right)\cdot\frac{\left(-3\right)}{\left(+4\right)}$$

$$k^2-2k+1$$

$$x^2+y=4$$

$$\int\frac{1}{5x}dx$$

$$\left(3-3y^2\right)$$