Solve 100x^2-160x+63=0

$$100 { x }^{ 2 } -160x+63=0$$

Solve for x

$$x=\frac{7}{10}=0.7$$

$$x=\frac{9}{10}=0.9$$

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.

$$100x^{2}-160x+63=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 100 for a, -160 for b, and 63 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-\left(-160\right)±\sqrt{\left(-160\right)^{2}-4\times 100\times 63}}{2\times 100}$$

Square -160.

$$x=\frac{-\left(-160\right)±\sqrt{25600-4\times 100\times 63}}{2\times 100}$$

Multiply -4 times 100.

$$x=\frac{-\left(-160\right)±\sqrt{25600-400\times 63}}{2\times 100}$$

Multiply -400 times 63.

$$x=\frac{-\left(-160\right)±\sqrt{25600-25200}}{2\times 100}$$

Add 25600 to -25200.

$$x=\frac{-\left(-160\right)±\sqrt{400}}{2\times 100}$$

Take the square root of 400.

$$x=\frac{-\left(-160\right)±20}{2\times 100}$$

The opposite of -160 is 160.

$$x=\frac{160±20}{2\times 100}$$

Multiply 2 times 100.

$$x=\frac{160±20}{200}$$

Now solve the equation x=\frac{160±20}{200} when ± is plus. Add 160 to 20.

$$x=\frac{180}{200}$$

Reduce the fraction \frac{180}{200} to lowest terms by extracting and canceling out 20.

$$x=\frac{9}{10}$$

Now solve the equation x=\frac{160±20}{200} when ± is minus. Subtract 20 from 160.

$$x=\frac{140}{200}$$

Reduce the fraction \frac{140}{200} to lowest terms by extracting and canceling out 20.

$$x=\frac{7}{10}$$

The equation is now solved.

$$x=\frac{9}{10} x=\frac{7}{10}$$

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.

$$100x^{2}-160x+63=0$$

Subtract 63 from both sides of the equation.

$$100x^{2}-160x+63-63=-63$$

Subtracting 63 from itself leaves 0.

$$100x^{2}-160x=-63$$

Divide both sides by 100.

$$\frac{100x^{2}-160x}{100}=-\frac{63}{100}$$

Dividing by 100 undoes the multiplication by 100.

$$x^{2}+\left(-\frac{160}{100}\right)x=-\frac{63}{100}$$

Reduce the fraction \frac{-160}{100} to lowest terms by extracting and canceling out 20.

$$x^{2}-\frac{8}{5}x=-\frac{63}{100}$$

Divide -\frac{8}{5}, the coefficient of the x term, by 2 to get -\frac{4}{5}. Then add the square of -\frac{4}{5} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$x^{2}-\frac{8}{5}x+\left(-\frac{4}{5}\right)^{2}=-\frac{63}{100}+\left(-\frac{4}{5}\right)^{2}$$

Square -\frac{4}{5} by squaring both the numerator and the denominator of the fraction.

$$x^{2}-\frac{8}{5}x+\frac{16}{25}=-\frac{63}{100}+\frac{16}{25}$$

Add -\frac{63}{100} to \frac{16}{25} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$x^{2}-\frac{8}{5}x+\frac{16}{25}=\frac{1}{100}$$

Factor x^{2}-\frac{8}{5}x+\frac{16}{25}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(x-\frac{4}{5}\right)^{2}=\frac{1}{100}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x-\frac{4}{5}\right)^{2}}=\sqrt{\frac{1}{100}}$$

Simplify.

$$x-\frac{4}{5}=\frac{1}{10} x-\frac{4}{5}=-\frac{1}{10}$$

Add \frac{4}{5} to both sides of the equation.

$$x=\frac{9}{10} x=\frac{7}{10}$$