Solve 2x(x-1)=x+9

$$2 x ( x - 1 ) = x + 9$$

Solve for x

$$x = -\frac{3}{2} = -1\frac{1}{2} = -1.5$$

$$x=3$$

Steps Using the Quadratic Formula

Use the distributive property to multiply 2x by x-1.

$$2x^{2}-2x=x+9$$

Subtract x from both sides.

$$2x^{2}-2x-x=9$$

Combine -2x and -x to get -3x.

$$2x^{2}-3x=9$$

Subtract 9 from both sides.

$$2x^{2}-3x-9=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 2 for a, -3 for b, and -9 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-\left(-3\right)±\sqrt{\left(-3\right)^{2}-4\times 2\left(-9\right)}}{2\times 2}$$

Square -3.

$$x=\frac{-\left(-3\right)±\sqrt{9-4\times 2\left(-9\right)}}{2\times 2}$$

Multiply -4 times 2.

$$x=\frac{-\left(-3\right)±\sqrt{9-8\left(-9\right)}}{2\times 2}$$

Multiply -8 times -9.

$$x=\frac{-\left(-3\right)±\sqrt{9+72}}{2\times 2}$$

Add 9 to 72.

$$x=\frac{-\left(-3\right)±\sqrt{81}}{2\times 2}$$

Take the square root of 81.

$$x=\frac{-\left(-3\right)±9}{2\times 2}$$

The opposite of -3 is 3.

$$x=\frac{3±9}{2\times 2}$$

Multiply 2 times 2.

$$x=\frac{3±9}{4}$$

Now solve the equation x=\frac{3±9}{4} when ± is plus. Add 3 to 9.

$$x=\frac{12}{4}$$

Divide 12 by 4.

$$x=3$$

Now solve the equation x=\frac{3±9}{4} when ± is minus. Subtract 9 from 3.

$$x=-\frac{6}{4}$$

Reduce the fraction \frac{-6}{4} to lowest terms by extracting and canceling out 2.

$$x=-\frac{3}{2}$$

The equation is now solved.

$$x=3 x=-\frac{3}{2}$$

Steps for Completing the Square

Use the distributive property to multiply 2x by x-1.

$$2x^{2}-2x=x+9$$

Subtract x from both sides.

$$2x^{2}-2x-x=9$$

Combine -2x and -x to get -3x.

$$2x^{2}-3x=9$$

Divide both sides by 2.

$$\frac{2x^{2}-3x}{2}=\frac{9}{2}$$

Dividing by 2 undoes the multiplication by 2.

$$x^{2}-\frac{3}{2}x=\frac{9}{2}$$

Divide -\frac{3}{2}, the coefficient of the x term, by 2 to get -\frac{3}{4}. Then add the square of -\frac{3}{4} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$x^{2}-\frac{3}{2}x+\left(-\frac{3}{4}\right)^{2}=\frac{9}{2}+\left(-\frac{3}{4}\right)^{2}$$

Square -\frac{3}{4} by squaring both the numerator and the denominator of the fraction.

$$x^{2}-\frac{3}{2}x+\frac{9}{16}=\frac{9}{2}+\frac{9}{16}$$

Add \frac{9}{2} to \frac{9}{16} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$x^{2}-\frac{3}{2}x+\frac{9}{16}=\frac{81}{16}$$

Factor x^{2}-\frac{3}{2}x+\frac{9}{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}.

$$\left(x-\frac{3}{4}\right)^{2}=\frac{81}{16}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x-\frac{3}{4}\right)^{2}}=\sqrt{\frac{81}{16}}$$

Simplify.

$$x-\frac{3}{4}=\frac{9}{4} x-\frac{3}{4}=-\frac{9}{4}$$

Add \frac{3}{4} to both sides of the equation.

$$x=3 x=-\frac{3}{2}$$