Solve 64x^2+32x=-4

$$64 x ^ { 2 } + 32 x = - 4$$

Solve for x

$$x=-\frac{1}{4}=-0.25$$

Steps Using Factoring By Grouping

Add 4 to both sides.

$$64x^{2}+32x+4=0$$

Divide both sides by 4.

$$16x^{2}+8x+1=0$$

To solve the equation, factor the left hand side by grouping. First, left hand side needs to be rewritten as 16x^{2}+ax+bx+1. To find a and b, set up a system to be solved.

$$a+b=8 ab=16\times 1=16$$

Since ab is positive, a and b have the same sign. Since a+b is positive, a and b are both positive. List all such integer pairs that give product 16.

$$1,16 2,8 4,4$$

Calculate the sum for each pair.

$$1+16=17 2+8=10 4+4=8$$

The solution is the pair that gives sum 8.

$$a=4 b=4$$

Rewrite 16x^{2}+8x+1 as \left(16x^{2}+4x\right)+\left(4x+1\right).

$$\left(16x^{2}+4x\right)+\left(4x+1\right)$$

Factor out 4x in 16x^{2}+4x.

$$4x\left(4x+1\right)+4x+1$$

Factor out common term 4x+1 by using distributive property.

$$\left(4x+1\right)\left(4x+1\right)$$

Rewrite as a binomial square.

$$\left(4x+1\right)^{2}$$

To find equation solution, solve 4x+1=0.

$$x=-\frac{1}{4}$$

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.

$$64x^{2}+32x=-4$$

Add 4 to both sides of the equation.

$$64x^{2}+32x-\left(-4\right)=-4-\left(-4\right)$$

Subtracting -4 from itself leaves 0.

$$64x^{2}+32x-\left(-4\right)=0$$

Subtract -4 from 0.

$$64x^{2}+32x+4=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 64 for a, 32 for b, and 4 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-32±\sqrt{32^{2}-4\times 64\times 4}}{2\times 64}$$

Square 32.

$$x=\frac{-32±\sqrt{1024-4\times 64\times 4}}{2\times 64}$$

Multiply -4 times 64.

$$x=\frac{-32±\sqrt{1024-256\times 4}}{2\times 64}$$

Multiply -256 times 4.

$$x=\frac{-32±\sqrt{1024-1024}}{2\times 64}$$

Add 1024 to -1024.

$$x=\frac{-32±\sqrt{0}}{2\times 64}$$

Take the square root of 0.

$$x=-\frac{32}{2\times 64}$$

Multiply 2 times 64.

$$x=-\frac{32}{128}$$

Reduce the fraction \frac{-32}{128} to lowest terms by extracting and canceling out 32.

$$x=-\frac{1}{4}$$

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.

$$64x^{2}+32x=-4$$

Divide both sides by 64.

$$\frac{64x^{2}+32x}{64}=-\frac{4}{64}$$

Dividing by 64 undoes the multiplication by 64.

$$x^{2}+\frac{32}{64}x=-\frac{4}{64}$$

Reduce the fraction \frac{32}{64} to lowest terms by extracting and canceling out 32.

$$x^{2}+\frac{1}{2}x=-\frac{4}{64}$$

Reduce the fraction \frac{-4}{64} to lowest terms by extracting and canceling out 4.

$$x^{2}+\frac{1}{2}x=-\frac{1}{16}$$

Divide \frac{1}{2}, the coefficient of the x term, by 2 to get \frac{1}{4}. Then add the square of \frac{1}{4} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$x^{2}+\frac{1}{2}x+\left(\frac{1}{4}\right)^{2}=-\frac{1}{16}+\left(\frac{1}{4}\right)^{2}$$

Square \frac{1}{4} by squaring both the numerator and the denominator of the fraction.

$$x^{2}+\frac{1}{2}x+\frac{1}{16}=\frac{-1+1}{16}$$

Add -\frac{1}{16} to \frac{1}{16} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$x^{2}+\frac{1}{2}x+\frac{1}{16}=0$$

Factor x^{2}+\frac{1}{2}x+\frac{1}{16}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(x+\frac{1}{4}\right)^{2}=0$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x+\frac{1}{4}\right)^{2}}=\sqrt{0}$$

Simplify.

$$x+\frac{1}{4}=0 x+\frac{1}{4}=0$$

Subtract \frac{1}{4} from both sides of the equation.

$$x=-\frac{1}{4} x=-\frac{1}{4}$$

The equation is now solved. Solutions are the same.

$$x=-\frac{1}{4}$$