Solve 6u^2-6-5u

$$6 u ^ { 2 } - 6 - 5 u$$

Factor

$$\left(2u-3\right)\left(3u+2\right)$$

Solution Steps

Rearrange the polynomial to put it in standard form. Place the terms in order from highest to lowest power.

$$6u^{2}-5u-6$$

Factor the expression by grouping. First, the expression needs to be rewritten as 6u^{2}+au+bu-6. To find a and b, set up a system to be solved.

$$a+b=-5 ab=6\left(-6\right)=-36$$

Since ab is negative, a and b have the opposite signs. Since a+b is negative, the negative number has greater absolute value than the positive. List all such integer pairs that give product -36.

$$1,-36 2,-18 3,-12 4,-9 6,-6$$

Calculate the sum for each pair.

$$1-36=-35 2-18=-16 3-12=-9 4-9=-5 6-6=0$$

The solution is the pair that gives sum -5.

$$a=-9 b=4$$

Rewrite 6u^{2}-5u-6 as \left(6u^{2}-9u\right)+\left(4u-6\right).

$$\left(6u^{2}-9u\right)+\left(4u-6\right)$$

Factor out 3u in the first and 2 in the second group.

$$3u\left(2u-3\right)+2\left(2u-3\right)$$

Factor out common term 2u-3 by using distributive property.

$$\left(2u-3\right)\left(3u+2\right)$$

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.

$$6u^{2}-5u-6=0$$

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.

$$u=\frac{-\left(-5\right)±\sqrt{\left(-5\right)^{2}-4\times 6\left(-6\right)}}{2\times 6}$$

Square -5.

$$u=\frac{-\left(-5\right)±\sqrt{25-4\times 6\left(-6\right)}}{2\times 6}$$

Multiply -4 times 6.

$$u=\frac{-\left(-5\right)±\sqrt{25-24\left(-6\right)}}{2\times 6}$$

Multiply -24 times -6.

$$u=\frac{-\left(-5\right)±\sqrt{25+144}}{2\times 6}$$

Add 25 to 144.

$$u=\frac{-\left(-5\right)±\sqrt{169}}{2\times 6}$$

Take the square root of 169.

$$u=\frac{-\left(-5\right)±13}{2\times 6}$$

The opposite of -5 is 5.

$$u=\frac{5±13}{2\times 6}$$

Multiply 2 times 6.

$$u=\frac{5±13}{12}$$

Now solve the equation u=\frac{5±13}{12} when ± is plus. Add 5 to 13.

$$u=\frac{18}{12}$$

Reduce the fraction \frac{18}{12} to lowest terms by extracting and canceling out 6.

$$u=\frac{3}{2}$$

Now solve the equation u=\frac{5±13}{12} when ± is minus. Subtract 13 from 5.

$$u=-\frac{8}{12}$$

Reduce the fraction \frac{-8}{12} to lowest terms by extracting and canceling out 4.

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

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

$$6u^{2}-5u-6=6\left(u-\frac{3}{2}\right)\left(u-\left(-\frac{2}{3}\right)\right)$$

Simplify all the expressions of the form p-\left(-q\right) to p+q.

$$6u^{2}-5u-6=6\left(u-\frac{3}{2}\right)\left(u+\frac{2}{3}\right)$$

Subtract \frac{3}{2} from u by finding a common denominator and subtracting the numerators. Then reduce the fraction to lowest terms if possible.

$$6u^{2}-5u-6=6\times \frac{2u-3}{2}\left(u+\frac{2}{3}\right)$$

Add \frac{2}{3} to u by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$6u^{2}-5u-6=6\times \frac{2u-3}{2}\times \frac{3u+2}{3}$$

Multiply \frac{2u-3}{2} times \frac{3u+2}{3} by multiplying numerator times numerator and denominator times denominator. Then reduce the fraction to lowest terms if possible.

$$6u^{2}-5u-6=6\times \frac{\left(2u-3\right)\left(3u+2\right)}{2\times 3}$$

Multiply 2 times 3.

$$6u^{2}-5u-6=6\times \frac{\left(2u-3\right)\left(3u+2\right)}{6}$$

Cancel out 6, the greatest common factor in 6 and 6.

$$6u^{2}-5u-6=\left(2u-3\right)\left(3u+2\right)$$

Evaluate

$$\left(2u-3\right)\left(3u+2\right)$$