Solve =-5x^2-16x

$$= - 5 x ^ { 2 } - 16 x$$

Factor

$$-x\left(5x+16\right)$$

Solution Steps

Factor out x.

$$x\left(-5x-16\right)$$

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.

$$-5x^{2}-16x=0$$

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.

$$x=\frac{-\left(-16\right)±\sqrt{\left(-16\right)^{2}}}{2\left(-5\right)}$$

Take the square root of \left(-16\right)^{2}.

$$x=\frac{-\left(-16\right)±16}{2\left(-5\right)}$$

The opposite of -16 is 16.

$$x=\frac{16±16}{2\left(-5\right)}$$

Multiply 2 times -5.

$$x=\frac{16±16}{-10}$$

Now solve the equation x=\frac{16±16}{-10} when ± is plus. Add 16 to 16.

$$x=\frac{32}{-10}$$

Reduce the fraction \frac{32}{-10} to lowest terms by extracting and canceling out 2.

$$x=-\frac{16}{5}$$

Now solve the equation x=\frac{16±16}{-10} when ± is minus. Subtract 16 from 16.

$$x=\frac{0}{-10}$$

Divide 0 by -10.

$$x=0$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute -\frac{16}{5} for x_{1} and 0 for x_{2}.

$$-5x^{2}-16x=-5\left(x-\left(-\frac{16}{5}\right)\right)x$$

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

$$-5x^{2}-16x=-5\left(x+\frac{16}{5}\right)x$$

Add \frac{16}{5} to x by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$-5x^{2}-16x=-5\times \frac{-5x-16}{-5}x$$

Cancel out 5, the greatest common factor in -5 and -5.

$$-5x^{2}-16x=\left(-5x-16\right)x$$

Evaluate

$$-x\left(5x+16\right)$$