Solve 28x^2+4x=0

$$28 x ^ { 2 } + 4 x = 0$$

Solve for x

$$x=-\frac{1}{7}\approx -0.142857143$$

$$x=0$$

Steps Using Factoring

Factor out x.

$$x\left(28x+4\right)=0$$

To find equation solutions, solve x=0 and 28x+4=0.

$$x=0 x=-\frac{1}{7}$$

Steps Using the Quadratic Formula

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.

$$28x^{2}+4x=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 28 for a, 4 for b, and 0 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-4±\sqrt{4^{2}}}{2\times 28}$$

Take the square root of 4^{2}.

$$x=\frac{-4±4}{2\times 28}$$

Multiply 2 times 28.

$$x=\frac{-4±4}{56}$$

Now solve the equation x=\frac{-4±4}{56} when ± is plus. Add -4 to 4.

$$x=\frac{0}{56}$$

Divide 0 by 56.

$$x=0$$

Now solve the equation x=\frac{-4±4}{56} when ± is minus. Subtract 4 from -4.

$$x=-\frac{8}{56}$$

Reduce the fraction \frac{-8}{56} to lowest terms by extracting and canceling out 8.

$$x=-\frac{1}{7}$$

The equation is now solved.

$$x=0 x=-\frac{1}{7}$$

Steps for Completing the Square

Quadratic equations such as this one can be solved by completing the square. In order to complete the square, the equation must first be in the form x^{2}+bx=c.

$$28x^{2}+4x=0$$

Divide both sides by 28.

$$\frac{28x^{2}+4x}{28}=\frac{0}{28}$$

Dividing by 28 undoes the multiplication by 28.

$$x^{2}+\frac{4}{28}x=\frac{0}{28}$$

Reduce the fraction \frac{4}{28} to lowest terms by extracting and canceling out 4.

$$x^{2}+\frac{1}{7}x=\frac{0}{28}$$

Divide 0 by 28.

$$x^{2}+\frac{1}{7}x=0$$

Divide \frac{1}{7}, the coefficient of the x term, by 2 to get \frac{1}{14}. Then add the square of \frac{1}{14} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$x^{2}+\frac{1}{7}x+\left(\frac{1}{14}\right)^{2}=\left(\frac{1}{14}\right)^{2}$$

Square \frac{1}{14} by squaring both the numerator and the denominator of the fraction.

$$x^{2}+\frac{1}{7}x+\frac{1}{196}=\frac{1}{196}$$

Factor x^{2}+\frac{1}{7}x+\frac{1}{196}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(x+\frac{1}{14}\right)^{2}=\frac{1}{196}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x+\frac{1}{14}\right)^{2}}=\sqrt{\frac{1}{196}}$$

Simplify.

$$x+\frac{1}{14}=\frac{1}{14} x+\frac{1}{14}=-\frac{1}{14}$$

Subtract \frac{1}{14} from both sides of the equation.

$$x=0 x=-\frac{1}{7}$$