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16x^{2}-12x-54=0
Subtract 54 from both sides.
8x^{2}-6x-27=0
Divide both sides by 2.
a+b=-6 ab=8\left(-27\right)=-216
To solve the equation, factor the left hand side by grouping. First, left hand side needs to be rewritten as 8x^{2}+ax+bx-27. To find a and b, set up a system to be solved.
1,-216 2,-108 3,-72 4,-54 6,-36 8,-27 9,-24 12,-18
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 -216.
1-216=-215 2-108=-106 3-72=-69 4-54=-50 6-36=-30 8-27=-19 9-24=-15 12-18=-6
Calculate the sum for each pair.
a=-18 b=12
The solution is the pair that gives sum -6.
\left(8x^{2}-18x\right)+\left(12x-27\right)
Rewrite 8x^{2}-6x-27 as \left(8x^{2}-18x\right)+\left(12x-27\right).
2x\left(4x-9\right)+3\left(4x-9\right)
Factor out 2x in the first and 3 in the second group.
\left(4x-9\right)\left(2x+3\right)
Factor out common term 4x-9 by using distributive property.
x=\frac{9}{4} x=-\frac{3}{2}
To find equation solutions, solve 4x-9=0 and 2x+3=0.
16x^{2}-12x=54
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.
16x^{2}-12x-54=54-54
Subtract 54 from both sides of the equation.
16x^{2}-12x-54=0
Subtracting 54 from itself leaves 0.
x=\frac{-\left(-12\right)±\sqrt{\left(-12\right)^{2}-4\times 16\left(-54\right)}}{2\times 16}
This equation is in standard form: ax^{2}+bx+c=0. Substitute 16 for a, -12 for b, and -54 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.
x=\frac{-\left(-12\right)±\sqrt{144-4\times 16\left(-54\right)}}{2\times 16}
Square -12.
x=\frac{-\left(-12\right)±\sqrt{144-64\left(-54\right)}}{2\times 16}
Multiply -4 times 16.
x=\frac{-\left(-12\right)±\sqrt{144+3456}}{2\times 16}
Multiply -64 times -54.
x=\frac{-\left(-12\right)±\sqrt{3600}}{2\times 16}
Add 144 to 3456.
x=\frac{-\left(-12\right)±60}{2\times 16}
Take the square root of 3600.
x=\frac{12±60}{2\times 16}
The opposite of -12 is 12.
x=\frac{12±60}{32}
Multiply 2 times 16.
x=\frac{72}{32}
Now solve the equation x=\frac{12±60}{32} when ± is plus. Add 12 to 60.
x=\frac{9}{4}
Reduce the fraction \frac{72}{32} to lowest terms by extracting and canceling out 8.
x=-\frac{48}{32}
Now solve the equation x=\frac{12±60}{32} when ± is minus. Subtract 60 from 12.
x=-\frac{3}{2}
Reduce the fraction \frac{-48}{32} to lowest terms by extracting and canceling out 16.
x=\frac{9}{4} x=-\frac{3}{2}
The equation is now solved.
16x^{2}-12x=54
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.
\frac{16x^{2}-12x}{16}=\frac{54}{16}
Divide both sides by 16.
x^{2}+\left(-\frac{12}{16}\right)x=\frac{54}{16}
Dividing by 16 undoes the multiplication by 16.
x^{2}-\frac{3}{4}x=\frac{54}{16}
Reduce the fraction \frac{-12}{16} to lowest terms by extracting and canceling out 4.
x^{2}-\frac{3}{4}x=\frac{27}{8}
Reduce the fraction \frac{54}{16} to lowest terms by extracting and canceling out 2.
x^{2}-\frac{3}{4}x+\left(-\frac{3}{8}\right)^{2}=\frac{27}{8}+\left(-\frac{3}{8}\right)^{2}
Divide -\frac{3}{4}, the coefficient of the x term, by 2 to get -\frac{3}{8}. Then add the square of -\frac{3}{8} to both sides of the equation. This step makes the left hand side of the equation a perfect square.
x^{2}-\frac{3}{4}x+\frac{9}{64}=\frac{27}{8}+\frac{9}{64}
Square -\frac{3}{8} by squaring both the numerator and the denominator of the fraction.
x^{2}-\frac{3}{4}x+\frac{9}{64}=\frac{225}{64}
Add \frac{27}{8} to \frac{9}{64} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.
\left(x-\frac{3}{8}\right)^{2}=\frac{225}{64}
Factor x^{2}-\frac{3}{4}x+\frac{9}{64}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.
\sqrt{\left(x-\frac{3}{8}\right)^{2}}=\sqrt{\frac{225}{64}}
Take the square root of both sides of the equation.
x-\frac{3}{8}=\frac{15}{8} x-\frac{3}{8}=-\frac{15}{8}
Simplify.
x=\frac{9}{4} x=-\frac{3}{2}
Add \frac{3}{8} to both sides of the equation.