Solve 5x^2-60x+800

$$5 x ^ { 2 } - 60 x + 800$$

Factor

$$5\left(x^{2}-12x+160\right)$$

Solution Steps

Factor out 5. Polynomial x^{2}-12x+160 is not factored since it does not have any rational roots.

$$5\left(x^{2}-12x+160\right)$$

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.

$$5x^{2}-60x+800=0$$

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.

$$x=\frac{-\left(-60\right)±\sqrt{\left(-60\right)^{2}-4\times 5\times 800}}{2\times 5}$$

Square -60.

$$x=\frac{-\left(-60\right)±\sqrt{3600-4\times 5\times 800}}{2\times 5}$$

Multiply -4 times 5.

$$x=\frac{-\left(-60\right)±\sqrt{3600-20\times 800}}{2\times 5}$$

Multiply -20 times 800.

$$x=\frac{-\left(-60\right)±\sqrt{3600-16000}}{2\times 5}$$

Add 3600 to -16000.

$$x=\frac{-\left(-60\right)±\sqrt{-12400}}{2\times 5}$$

Since the square root of a negative number is not defined in the real field, there are no solutions. Quadratic polynomial cannot be factored.

$$5x^{2}-60x+800$$

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 5

$$x ^ 2 -12x +160 = 0$$

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

$$r + s = 12 rs = 160$$

Two numbers r and s sum up to 12 exactly when the average of the two numbers is \frac{1}{2}*12 = 6. 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>

$$r = 6 - u s = 6 + u$$

To solve for unknown quantity u, substitute these in the product equation rs = 160

$$(6 - u) (6 + u) = 160$$

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

$$36 - u^2 = 160$$

Simplify the expression by subtracting 36 on both sides

$$-u^2 = 160-36 = 124$$

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

$$u^2 = -124 u = \pm\sqrt{-124} = \pm \sqrt{124}i$$

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

$$r =6 - \sqrt{124}i s = 6 + \sqrt{124}i$$

Evaluate

$$5\left(x^{2}-12x+160\right)$$