Solve -1*r^2-2r

$$- 1 \times r ^ { 2 } - 2 r$$

Factor

$$-r\left(r+2\right)$$

Solution Steps

Factor out r.

$$r\left(-r-2\right)$$

Steps Using the Quadratic Formula

Quadratic polynomial can be factored using the transformation ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right), where x_{1} and x_{2} are the solutions of the quadratic equation ax^{2}+bx+c=0.

$$-r^{2}-2r=0$$

All equations of the form ax^{2}+bx+c=0 can be solved using the quadratic formula: \frac{-b±\sqrt{b^{2}-4ac}}{2a}. The quadratic formula gives two solutions, one when ± is addition and one when it is subtraction.

$$r=\frac{-\left(-2\right)±\sqrt{\left(-2\right)^{2}}}{2\left(-1\right)}$$

Take the square root of \left(-2\right)^{2}.

$$r=\frac{-\left(-2\right)±2}{2\left(-1\right)}$$

The opposite of -2 is 2.

$$r=\frac{2±2}{2\left(-1\right)}$$

Multiply 2 times -1.

$$r=\frac{2±2}{-2}$$

Now solve the equation r=\frac{2±2}{-2} when ± is plus. Add 2 to 2.

$$r=\frac{4}{-2}$$

Divide 4 by -2.

$$r=-2$$

Now solve the equation r=\frac{2±2}{-2} when ± is minus. Subtract 2 from 2.

$$r=\frac{0}{-2}$$

Divide 0 by -2.

$$r=0$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute -2 for x_{1} and 0 for x_{2}.

$$-r^{2}-2r=-\left(r-\left(-2\right)\right)r$$

Simplify all the expressions of the form p-\left(-q\right) to p+q.

$$-r^{2}-2r=-\left(r+2\right)r$$

Evaluate

$$-r\left(r+2\right)$$