Solve 4w+16w^2=80

$$4 w + 16 w ^ { 2 } = 80$$

Solve for w

$$w = \frac{\sqrt{321} - 1}{8} \approx 2.114559108$$

$$w=\frac{-\sqrt{321}-1}{8}\approx -2.364559108$$

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.

$$16w^{2}+4w=80$$

Subtract 80 from both sides of the equation.

$$16w^{2}+4w-80=80-80$$

Subtracting 80 from itself leaves 0.

$$16w^{2}+4w-80=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 16 for a, 4 for b, and -80 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$w=\frac{-4±\sqrt{4^{2}-4\times 16\left(-80\right)}}{2\times 16}$$

Square 4.

$$w=\frac{-4±\sqrt{16-4\times 16\left(-80\right)}}{2\times 16}$$

Multiply -4 times 16.

$$w=\frac{-4±\sqrt{16-64\left(-80\right)}}{2\times 16}$$

Multiply -64 times -80.

$$w=\frac{-4±\sqrt{16+5120}}{2\times 16}$$

Add 16 to 5120.

$$w=\frac{-4±\sqrt{5136}}{2\times 16}$$

Take the square root of 5136.

$$w=\frac{-4±4\sqrt{321}}{2\times 16}$$

Multiply 2 times 16.

$$w=\frac{-4±4\sqrt{321}}{32}$$

Now solve the equation w=\frac{-4±4\sqrt{321}}{32} when ± is plus. Add -4 to 4\sqrt{321}.

$$w=\frac{4\sqrt{321}-4}{32}$$

Divide -4+4\sqrt{321} by 32.

$$w=\frac{\sqrt{321}-1}{8}$$

Now solve the equation w=\frac{-4±4\sqrt{321}}{32} when ± is minus. Subtract 4\sqrt{321} from -4.

$$w=\frac{-4\sqrt{321}-4}{32}$$

Divide -4-4\sqrt{321} by 32.

$$w=\frac{-\sqrt{321}-1}{8}$$

The equation is now solved.

$$w=\frac{\sqrt{321}-1}{8} w=\frac{-\sqrt{321}-1}{8}$$

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.

$$16w^{2}+4w=80$$

Divide both sides by 16.

$$\frac{16w^{2}+4w}{16}=\frac{80}{16}$$

Dividing by 16 undoes the multiplication by 16.

$$w^{2}+\frac{4}{16}w=\frac{80}{16}$$

Reduce the fraction \frac{4}{16} to lowest terms by extracting and canceling out 4.

$$w^{2}+\frac{1}{4}w=\frac{80}{16}$$

Divide 80 by 16.

$$w^{2}+\frac{1}{4}w=5$$

Divide \frac{1}{4}, the coefficient of the x term, by 2 to get \frac{1}{8}. Then add the square of \frac{1}{8} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$w^{2}+\frac{1}{4}w+\left(\frac{1}{8}\right)^{2}=5+\left(\frac{1}{8}\right)^{2}$$

Square \frac{1}{8} by squaring both the numerator and the denominator of the fraction.

$$w^{2}+\frac{1}{4}w+\frac{1}{64}=5+\frac{1}{64}$$

Add 5 to \frac{1}{64}.

$$w^{2}+\frac{1}{4}w+\frac{1}{64}=\frac{321}{64}$$

Factor w^{2}+\frac{1}{4}w+\frac{1}{64}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(w+\frac{1}{8}\right)^{2}=\frac{321}{64}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(w+\frac{1}{8}\right)^{2}}=\sqrt{\frac{321}{64}}$$

Simplify.

$$w+\frac{1}{8}=\frac{\sqrt{321}}{8} w+\frac{1}{8}=-\frac{\sqrt{321}}{8}$$

Subtract \frac{1}{8} from both sides of the equation.

$$w=\frac{\sqrt{321}-1}{8} w=\frac{-\sqrt{321}-1}{8}$$