Solve 3x^2-9x

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

Factor

$$3x\left(x-3\right)$$

Solution Steps

Factor out 3.

$$3\left(x^{2}-3x\right)$$

Consider x^{2}-3x. Factor out x.

$$x\left(x-3\right)$$

Rewrite the complete factored expression.

$$3x\left(x-3\right)$$

Steps Using the Quadratic Formula

Quadratic polynomial can be factored using the transformation ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right), where x_{1} and x_{2} are the solutions of the quadratic equation ax^{2}+bx+c=0.

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

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.

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

Take the square root of \left(-9\right)^{2}.

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

The opposite of -9 is 9.

$$x=\frac{9±9}{2\times 3}$$

Multiply 2 times 3.

$$x=\frac{9±9}{6}$$

Now solve the equation x=\frac{9±9}{6} when ± is plus. Add 9 to 9.

$$x=\frac{18}{6}$$

Divide 18 by 6.

$$x=3$$

Now solve the equation x=\frac{9±9}{6} when ± is minus. Subtract 9 from 9.

$$x=\frac{0}{6}$$

Divide 0 by 6.

$$x=0$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute 3 for x_{1} and 0 for x_{2}.

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

Evaluate

$$3x\left(x-3\right)$$