Solve 48x^2+22x-15=0

$$48 { x }^{ 2 } +22x-15=0$$

Solve for x

$$x=-\frac{5}{6}\approx -0.833333333$$

$$x=\frac{3}{8}=0.375$$

Steps Using Factoring By Grouping

To solve the equation, factor the left hand side by grouping. First, left hand side needs to be rewritten as 48x^{2}+ax+bx-15. To find a and b, set up a system to be solved.

$$a+b=22 ab=48\left(-15\right)=-720$$

Since ab is negative, a and b have the opposite signs. Since a+b is positive, the positive number has greater absolute value than the negative. List all such integer pairs that give product -720.

$$-1,720 -2,360 -3,240 -4,180 -5,144 -6,120 -8,90 -9,80 -10,72 -12,60 -15,48 -16,45 -18,40 -20,36 -24,30$$

Calculate the sum for each pair.

$$-1+720=719 -2+360=358 -3+240=237 -4+180=176 -5+144=139 -6+120=114 -8+90=82 -9+80=71 -10+72=62 -12+60=48 -15+48=33 -16+45=29 -18+40=22 -20+36=16 -24+30=6$$

The solution is the pair that gives sum 22.

$$a=-18 b=40$$

Rewrite 48x^{2}+22x-15 as \left(48x^{2}-18x\right)+\left(40x-15\right).

$$\left(48x^{2}-18x\right)+\left(40x-15\right)$$

Factor out 6x in the first and 5 in the second group.

$$6x\left(8x-3\right)+5\left(8x-3\right)$$

Factor out common term 8x-3 by using distributive property.

$$\left(8x-3\right)\left(6x+5\right)$$

To find equation solutions, solve 8x-3=0 and 6x+5=0.

$$x=\frac{3}{8} x=-\frac{5}{6}$$

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.

$$48x^{2}+22x-15=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 48 for a, 22 for b, and -15 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-22±\sqrt{22^{2}-4\times 48\left(-15\right)}}{2\times 48}$$

Square 22.

$$x=\frac{-22±\sqrt{484-4\times 48\left(-15\right)}}{2\times 48}$$

Multiply -4 times 48.

$$x=\frac{-22±\sqrt{484-192\left(-15\right)}}{2\times 48}$$

Multiply -192 times -15.

$$x=\frac{-22±\sqrt{484+2880}}{2\times 48}$$

Add 484 to 2880.

$$x=\frac{-22±\sqrt{3364}}{2\times 48}$$

Take the square root of 3364.

$$x=\frac{-22±58}{2\times 48}$$

Multiply 2 times 48.

$$x=\frac{-22±58}{96}$$

Now solve the equation x=\frac{-22±58}{96} when ± is plus. Add -22 to 58.

$$x=\frac{36}{96}$$

Reduce the fraction \frac{36}{96} to lowest terms by extracting and canceling out 12.

$$x=\frac{3}{8}$$

Now solve the equation x=\frac{-22±58}{96} when ± is minus. Subtract 58 from -22.

$$x=-\frac{80}{96}$$

Reduce the fraction \frac{-80}{96} to lowest terms by extracting and canceling out 16.

$$x=-\frac{5}{6}$$

The equation is now solved.

$$x=\frac{3}{8} x=-\frac{5}{6}$$

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.

$$48x^{2}+22x-15=0$$

Add 15 to both sides of the equation.

$$48x^{2}+22x-15-\left(-15\right)=-\left(-15\right)$$

Subtracting -15 from itself leaves 0.

$$48x^{2}+22x=-\left(-15\right)$$

Subtract -15 from 0.

$$48x^{2}+22x=15$$

Divide both sides by 48.

$$\frac{48x^{2}+22x}{48}=\frac{15}{48}$$

Dividing by 48 undoes the multiplication by 48.

$$x^{2}+\frac{22}{48}x=\frac{15}{48}$$

Reduce the fraction \frac{22}{48} to lowest terms by extracting and canceling out 2.

$$x^{2}+\frac{11}{24}x=\frac{15}{48}$$

Reduce the fraction \frac{15}{48} to lowest terms by extracting and canceling out 3.

$$x^{2}+\frac{11}{24}x=\frac{5}{16}$$

Divide \frac{11}{24}, the coefficient of the x term, by 2 to get \frac{11}{48}. Then add the square of \frac{11}{48} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$x^{2}+\frac{11}{24}x+\left(\frac{11}{48}\right)^{2}=\frac{5}{16}+\left(\frac{11}{48}\right)^{2}$$

Square \frac{11}{48} by squaring both the numerator and the denominator of the fraction.

$$x^{2}+\frac{11}{24}x+\frac{121}{2304}=\frac{5}{16}+\frac{121}{2304}$$

Add \frac{5}{16} to \frac{121}{2304} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$x^{2}+\frac{11}{24}x+\frac{121}{2304}=\frac{841}{2304}$$

Factor x^{2}+\frac{11}{24}x+\frac{121}{2304}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(x+\frac{11}{48}\right)^{2}=\frac{841}{2304}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x+\frac{11}{48}\right)^{2}}=\sqrt{\frac{841}{2304}}$$

Simplify.

$$x+\frac{11}{48}=\frac{29}{48} x+\frac{11}{48}=-\frac{29}{48}$$

Subtract \frac{11}{48} from both sides of the equation.

$$x=\frac{3}{8} x=-\frac{5}{6}$$