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x^{2}+3x-15=0
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.
x=\frac{-3±\sqrt{3^{2}-4\left(-15\right)}}{2}
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{-3±\sqrt{9-4\left(-15\right)}}{2}
Square 3.
x=\frac{-3±\sqrt{9+60}}{2}
Multiply -4 times -15.
x=\frac{-3±\sqrt{69}}{2}
Add 9 to 60.
x=\frac{\sqrt{69}-3}{2}
Now solve the equation x=\frac{-3±\sqrt{69}}{2} when ± is plus. Add -3 to \sqrt{69}.
x=\frac{-\sqrt{69}-3}{2}
Now solve the equation x=\frac{-3±\sqrt{69}}{2} when ± is minus. Subtract \sqrt{69} from -3.
x^{2}+3x-15=\left(x-\frac{\sqrt{69}-3}{2}\right)\left(x-\frac{-\sqrt{69}-3}{2}\right)
Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute \frac{-3+\sqrt{69}}{2} for x_{1} and \frac{-3-\sqrt{69}}{2} for x_{2}.
x ^ 2 +3x -15 = 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 = -3 rs = -15
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{3}{2} - u s = -\frac{3}{2} + u
Two numbers r and s sum up to -3 exactly when the average of the two numbers is \frac{1}{2}*-3 = -\frac{3}{2}. 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{3}{2} - u) (-\frac{3}{2} + u) = -15
To solve for unknown quantity u, substitute these in the product equation rs = -15
\frac{9}{4} - u^2 = -15
Simplify by expanding (a -b) (a + b) = a^2 – b^2
-u^2 = -15-\frac{9}{4} = -\frac{69}{4}
Simplify the expression by subtracting \frac{9}{4} on both sides
u^2 = \frac{69}{4} u = \pm\sqrt{\frac{69}{4}} = \pm \frac{\sqrt{69}}{2}
Simplify the expression by multiplying -1 on both sides and take the square root to obtain the value of unknown variable u
r =-\frac{3}{2} - \frac{\sqrt{69}}{2} = -5.653 s = -\frac{3}{2} + \frac{\sqrt{69}}{2} = 2.653
The factors r and s are the solutions to the quadratic equation. Substitute the value of u to compute the r and s.