Solve -2x^2+40x

$$- 2 x ^ { 2 } + 40 x$$

Factor

$$2x\left(20-x\right)$$

Solution Steps

Factor out 2.

$$2\left(-x^{2}+20x\right)$$

Consider -x^{2}+20x. Factor out x.

$$x\left(-x+20\right)$$

Rewrite the complete factored expression.

$$2x\left(-x+20\right)$$

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.

$$-2x^{2}+40x=0$$

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.

$$x=\frac{-40±\sqrt{40^{2}}}{2\left(-2\right)}$$

Take the square root of 40^{2}.

$$x=\frac{-40±40}{2\left(-2\right)}$$

Multiply 2 times -2.

$$x=\frac{-40±40}{-4}$$

Now solve the equation x=\frac{-40±40}{-4} when ± is plus. Add -40 to 40.

$$x=\frac{0}{-4}$$

Divide 0 by -4.

$$x=0$$

Now solve the equation x=\frac{-40±40}{-4} when ± is minus. Subtract 40 from -40.

$$x=-\frac{80}{-4}$$

Divide -80 by -4.

$$x=20$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute 0 for x_{1} and 20 for x_{2}.

$$-2x^{2}+40x=-2x\left(x-20\right)$$

Evaluate

$$2x\left(20-x\right)$$