Solve 2x^2-14x-155

$$2 x ^ { 2 } - 14 x - 155$$

Factor

$$2\left(x-\frac{7-\sqrt{359}}{2}\right)\left(x-\frac{\sqrt{359}+7}{2}\right)$$

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.

$$2x^{2}-14x-155=0$$

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.

$$x=\frac{-\left(-14\right)±\sqrt{\left(-14\right)^{2}-4\times 2\left(-155\right)}}{2\times 2}$$

Square -14.

$$x=\frac{-\left(-14\right)±\sqrt{196-4\times 2\left(-155\right)}}{2\times 2}$$

Multiply -4 times 2.

$$x=\frac{-\left(-14\right)±\sqrt{196-8\left(-155\right)}}{2\times 2}$$

Multiply -8 times -155.

$$x=\frac{-\left(-14\right)±\sqrt{196+1240}}{2\times 2}$$

Add 196 to 1240.

$$x=\frac{-\left(-14\right)±\sqrt{1436}}{2\times 2}$$

Take the square root of 1436.

$$x=\frac{-\left(-14\right)±2\sqrt{359}}{2\times 2}$$

The opposite of -14 is 14.

$$x=\frac{14±2\sqrt{359}}{2\times 2}$$

Multiply 2 times 2.

$$x=\frac{14±2\sqrt{359}}{4}$$

Now solve the equation x=\frac{14±2\sqrt{359}}{4} when ± is plus. Add 14 to 2\sqrt{359}.

$$x=\frac{2\sqrt{359}+14}{4}$$

Divide 14+2\sqrt{359} by 4.

$$x=\frac{\sqrt{359}+7}{2}$$

Now solve the equation x=\frac{14±2\sqrt{359}}{4} when ± is minus. Subtract 2\sqrt{359} from 14.

$$x=\frac{14-2\sqrt{359}}{4}$$

Divide 14-2\sqrt{359} by 4.

$$x=\frac{7-\sqrt{359}}{2}$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute \frac{7+\sqrt{359}}{2} for x_{1} and \frac{7-\sqrt{359}}{2} for x_{2}.

$$2x^{2}-14x-155=2\left(x-\frac{\sqrt{359}+7}{2}\right)\left(x-\frac{7-\sqrt{359}}{2}\right)$$

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 2

$$x ^ 2 -7x -\frac{155}{2} = 0$$

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

$$r + s = 7 rs = -\frac{155}{2}$$

Two numbers r and s sum up to 7 exactly when the average of the two numbers is \frac{1}{2}*7 = \frac{7}{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>

$$r = \frac{7}{2} - u s = \frac{7}{2} + u$$

To solve for unknown quantity u, substitute these in the product equation rs = -\frac{155}{2}

$$(\frac{7}{2} - u) (\frac{7}{2} + u) = -\frac{155}{2}$$

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

$$\frac{49}{4} - u^2 = -\frac{155}{2}$$

Simplify the expression by subtracting \frac{49}{4} on both sides

$$-u^2 = -\frac{155}{2}-\frac{49}{4} = -\frac{359}{4}$$

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

$$u^2 = \frac{359}{4} u = \pm\sqrt{\frac{359}{4}} = \pm \frac{\sqrt{359}}{2}$$

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

$$r =\frac{7}{2} - \frac{\sqrt{359}}{2} = -5.974 s = \frac{7}{2} + \frac{\sqrt{359}}{2} = 12.974$$

Evaluate

$$2x^{2}-14x-155$$