Solve {l}{3x^2-20x}{-339}

$$\left. \begin{array} { l } { 3 x ^ { 2 } - 20 x } \\ { - 339 } \end{array} \right.$$

Factor

$$3\left(x-\frac{10-\sqrt{1117}}{3}\right)\left(x-\frac{\sqrt{1117}+10}{3}\right)$$

Steps Using the Quadratic Formula

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.

$$3x^{2}-20x-339=0$$

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.

$$x=\frac{-\left(-20\right)±\sqrt{\left(-20\right)^{2}-4\times 3\left(-339\right)}}{2\times 3}$$

Square -20.

$$x=\frac{-\left(-20\right)±\sqrt{400-4\times 3\left(-339\right)}}{2\times 3}$$

Multiply -4 times 3.

$$x=\frac{-\left(-20\right)±\sqrt{400-12\left(-339\right)}}{2\times 3}$$

Multiply -12 times -339.

$$x=\frac{-\left(-20\right)±\sqrt{400+4068}}{2\times 3}$$

Add 400 to 4068.

$$x=\frac{-\left(-20\right)±\sqrt{4468}}{2\times 3}$$

Take the square root of 4468.

$$x=\frac{-\left(-20\right)±2\sqrt{1117}}{2\times 3}$$

The opposite of -20 is 20.

$$x=\frac{20±2\sqrt{1117}}{2\times 3}$$

Multiply 2 times 3.

$$x=\frac{20±2\sqrt{1117}}{6}$$

Now solve the equation x=\frac{20±2\sqrt{1117}}{6} when ± is plus. Add 20 to 2\sqrt{1117}.

$$x=\frac{2\sqrt{1117}+20}{6}$$

Divide 20+2\sqrt{1117} by 6.

$$x=\frac{\sqrt{1117}+10}{3}$$

Now solve the equation x=\frac{20±2\sqrt{1117}}{6} when ± is minus. Subtract 2\sqrt{1117} from 20.

$$x=\frac{20-2\sqrt{1117}}{6}$$

Divide 20-2\sqrt{1117} by 6.

$$x=\frac{10-\sqrt{1117}}{3}$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute \frac{10+\sqrt{1117}}{3} for x_{1} and \frac{10-\sqrt{1117}}{3} for x_{2}.

$$3x^{2}-20x-339=3\left(x-\frac{\sqrt{1117}+10}{3}\right)\left(x-\frac{10-\sqrt{1117}}{3}\right)$$

Steps Using Direct Factoring Method

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.This is achieved by dividing both sides of the equation by 3

$$x ^ 2 -\frac{20}{3}x -113 = 0$$

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

$$r + s = \frac{20}{3} rs = -113$$

Two numbers r and s sum up to \frac{20}{3} exactly when the average of the two numbers is \frac{1}{2}*\frac{20}{3} = \frac{10}{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>

$$r = \frac{10}{3} - u s = \frac{10}{3} + u$$

To solve for unknown quantity u, substitute these in the product equation rs = -113

$$(\frac{10}{3} - u) (\frac{10}{3} + u) = -113$$

Simplify by expanding (a -b) (a + b) = a^2 – b^2

$$\frac{100}{9} - u^2 = -113$$

Simplify the expression by subtracting \frac{100}{9} on both sides

$$-u^2 = -113-\frac{100}{9} = -\frac{1117}{9}$$

Simplify the expression by multiplying -1 on both sides and take the square root to obtain the value of unknown variable u

$$u^2 = \frac{1117}{9} u = \pm\sqrt{\frac{1117}{9}} = \pm \frac{\sqrt{1117}}{3}$$

The factors r and s are the solutions to the quadratic equation. Substitute the value of u to compute the r and s.

$$r =\frac{10}{3} - \frac{\sqrt{1117}}{3} = -7.807 s = \frac{10}{3} + \frac{\sqrt{1117}}{3} = 14.474$$

Evaluate

$$3x^{2}-20x-339$$