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3x^{2}+20x-60=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{-20±\sqrt{20^{2}-4\times 3\left(-60\right)}}{2\times 3}
This equation is in standard form: ax^{2}+bx+c=0. Substitute 3 for a, 20 for b, and -60 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.
x=\frac{-20±\sqrt{400-4\times 3\left(-60\right)}}{2\times 3}
Square 20.
x=\frac{-20±\sqrt{400-12\left(-60\right)}}{2\times 3}
Multiply -4 times 3.
x=\frac{-20±\sqrt{400+720}}{2\times 3}
Multiply -12 times -60.
x=\frac{-20±\sqrt{1120}}{2\times 3}
Add 400 to 720.
x=\frac{-20±4\sqrt{70}}{2\times 3}
Take the square root of 1120.
x=\frac{-20±4\sqrt{70}}{6}
Multiply 2 times 3.
x=\frac{4\sqrt{70}-20}{6}
Now solve the equation x=\frac{-20±4\sqrt{70}}{6} when ± is plus. Add -20 to 4\sqrt{70}.
x=\frac{2\sqrt{70}-10}{3}
Divide -20+4\sqrt{70} by 6.
x=\frac{-4\sqrt{70}-20}{6}
Now solve the equation x=\frac{-20±4\sqrt{70}}{6} when ± is minus. Subtract 4\sqrt{70} from -20.
x=\frac{-2\sqrt{70}-10}{3}
Divide -20-4\sqrt{70} by 6.
x=\frac{2\sqrt{70}-10}{3} x=\frac{-2\sqrt{70}-10}{3}
The equation is now solved.
3x^{2}+20x-60=0
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.
3x^{2}+20x-60-\left(-60\right)=-\left(-60\right)
Add 60 to both sides of the equation.
3x^{2}+20x=-\left(-60\right)
Subtracting -60 from itself leaves 0.
3x^{2}+20x=60
Subtract -60 from 0.
\frac{3x^{2}+20x}{3}=\frac{60}{3}
Divide both sides by 3.
x^{2}+\frac{20}{3}x=\frac{60}{3}
Dividing by 3 undoes the multiplication by 3.
x^{2}+\frac{20}{3}x=20
Divide 60 by 3.
x^{2}+\frac{20}{3}x+\left(\frac{10}{3}\right)^{2}=20+\left(\frac{10}{3}\right)^{2}
Divide \frac{20}{3}, the coefficient of the x term, by 2 to get \frac{10}{3}. Then add the square of \frac{10}{3} to both sides of the equation. This step makes the left hand side of the equation a perfect square.
x^{2}+\frac{20}{3}x+\frac{100}{9}=20+\frac{100}{9}
Square \frac{10}{3} by squaring both the numerator and the denominator of the fraction.
x^{2}+\frac{20}{3}x+\frac{100}{9}=\frac{280}{9}
Add 20 to \frac{100}{9}.
\left(x+\frac{10}{3}\right)^{2}=\frac{280}{9}
Factor x^{2}+\frac{20}{3}x+\frac{100}{9}. 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{10}{3}\right)^{2}}=\sqrt{\frac{280}{9}}
Take the square root of both sides of the equation.
x+\frac{10}{3}=\frac{2\sqrt{70}}{3} x+\frac{10}{3}=-\frac{2\sqrt{70}}{3}
Simplify.
x=\frac{2\sqrt{70}-10}{3} x=\frac{-2\sqrt{70}-10}{3}
Subtract \frac{10}{3} from both sides of the equation.