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-3x^{2}+8x-7=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{-8±\sqrt{8^{2}-4\left(-3\right)\left(-7\right)}}{2\left(-3\right)}
This equation is in standard form: ax^{2}+bx+c=0. Substitute -3 for a, 8 for b, and -7 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.
x=\frac{-8±\sqrt{64-4\left(-3\right)\left(-7\right)}}{2\left(-3\right)}
Square 8.
x=\frac{-8±\sqrt{64+12\left(-7\right)}}{2\left(-3\right)}
Multiply -4 times -3.
x=\frac{-8±\sqrt{64-84}}{2\left(-3\right)}
Multiply 12 times -7.
x=\frac{-8±\sqrt{-20}}{2\left(-3\right)}
Add 64 to -84.
x=\frac{-8±2\sqrt{5}i}{2\left(-3\right)}
Take the square root of -20.
x=\frac{-8±2\sqrt{5}i}{-6}
Multiply 2 times -3.
x=\frac{-8+2\sqrt{5}i}{-6}
Now solve the equation x=\frac{-8±2\sqrt{5}i}{-6} when ± is plus. Add -8 to 2i\sqrt{5}.
x=\frac{-\sqrt{5}i+4}{3}
Divide -8+2i\sqrt{5} by -6.
x=\frac{-2\sqrt{5}i-8}{-6}
Now solve the equation x=\frac{-8±2\sqrt{5}i}{-6} when ± is minus. Subtract 2i\sqrt{5} from -8.
x=\frac{4+\sqrt{5}i}{3}
Divide -8-2i\sqrt{5} by -6.
x=\frac{-\sqrt{5}i+4}{3} x=\frac{4+\sqrt{5}i}{3}
The equation is now solved.
-3x^{2}+8x-7=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}+8x-7-\left(-7\right)=-\left(-7\right)
Add 7 to both sides of the equation.
-3x^{2}+8x=-\left(-7\right)
Subtracting -7 from itself leaves 0.
-3x^{2}+8x=7
Subtract -7 from 0.
\frac{-3x^{2}+8x}{-3}=\frac{7}{-3}
Divide both sides by -3.
x^{2}+\frac{8}{-3}x=\frac{7}{-3}
Dividing by -3 undoes the multiplication by -3.
x^{2}-\frac{8}{3}x=\frac{7}{-3}
Divide 8 by -3.
x^{2}-\frac{8}{3}x=-\frac{7}{3}
Divide 7 by -3.
x^{2}-\frac{8}{3}x+\left(-\frac{4}{3}\right)^{2}=-\frac{7}{3}+\left(-\frac{4}{3}\right)^{2}
Divide -\frac{8}{3}, the coefficient of the x term, by 2 to get -\frac{4}{3}. Then add the square of -\frac{4}{3} to both sides of the equation. This step makes the left hand side of the equation a perfect square.
x^{2}-\frac{8}{3}x+\frac{16}{9}=-\frac{7}{3}+\frac{16}{9}
Square -\frac{4}{3} by squaring both the numerator and the denominator of the fraction.
x^{2}-\frac{8}{3}x+\frac{16}{9}=-\frac{5}{9}
Add -\frac{7}{3} to \frac{16}{9} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.
\left(x-\frac{4}{3}\right)^{2}=-\frac{5}{9}
Factor x^{2}-\frac{8}{3}x+\frac{16}{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{4}{3}\right)^{2}}=\sqrt{-\frac{5}{9}}
Take the square root of both sides of the equation.
x-\frac{4}{3}=\frac{\sqrt{5}i}{3} x-\frac{4}{3}=-\frac{\sqrt{5}i}{3}
Simplify.
x=\frac{4+\sqrt{5}i}{3} x=\frac{-\sqrt{5}i+4}{3}
Add \frac{4}{3} to both sides of the equation.
x ^ 2 -\frac{8}{3}x +\frac{7}{3} = 0
Quadratic equations such as this one can be solved by a new direct factoring method that does not require guess work. To use the direct factoring method, the equation must be in the form x^2+Bx+C=0.
r + s = \frac{8}{3} rs = \frac{7}{3}
Let r and s be the factors for the quadratic equation such that x^2+Bx+C=(x−r)(x−s) where sum of factors (r+s)=−B and the product of factors rs = C
r = \frac{4}{3} - u s = \frac{4}{3} + u
Two numbers r and s sum up to \frac{8}{3} exactly when the average of the two numbers is \frac{1}{2}*\frac{8}{3} = \frac{4}{3}. You can also see that the midpoint of r and s corresponds to the axis of symmetry of the parabola represented by the quadratic equation y=x^2+Bx+C. The values of r and s are equidistant from the center by an unknown quantity u. Express r and s with respect to variable u. <div style='padding: 8px'><img src='https://opalmath.azureedge.net/customsolver/quadraticgraph.png' style='width: 100%;max-width: 700px' /></div>
(\frac{4}{3} - u) (\frac{4}{3} + u) = \frac{7}{3}
To solve for unknown quantity u, substitute these in the product equation rs = \frac{7}{3}
\frac{16}{9} - u^2 = \frac{7}{3}
Simplify by expanding (a -b) (a + b) = a^2 – b^2
-u^2 = \frac{7}{3}-\frac{16}{9} = \frac{5}{9}
Simplify the expression by subtracting \frac{16}{9} on both sides
u^2 = -\frac{5}{9} u = \pm\sqrt{-\frac{5}{9}} = \pm \frac{\sqrt{5}}{3}i
Simplify the expression by multiplying -1 on both sides and take the square root to obtain the value of unknown variable u
r =\frac{4}{3} - \frac{\sqrt{5}}{3}i = 1.333 - 0.745i s = \frac{4}{3} + \frac{\sqrt{5}}{3}i = 1.333 + 0.745i
The factors r and s are the solutions to the quadratic equation. Substitute the value of u to compute the r and s.