Solve 0quadx^2-2x-15=0

$$0 \quad x ^ { 2 } - 2 x - 15 = 0$$

Solve for x

$$x = -\frac{15}{2} = -7\frac{1}{2} = -7.5$$

Steps for Solving Linear Equation

Anything times zero gives zero.

$$0-2x-15=0$$

Subtract 15 from 0 to get -15.

$$-15-2x=0$$

Add 15 to both sides. Anything plus zero gives itself.

$$-2x=15$$

Divide both sides by -2.

$$x=\frac{15}{-2}$$

Fraction \frac{15}{-2} can be rewritten as -\frac{15}{2} by extracting the negative sign.

$$x=-\frac{15}{2}$$

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.

$$x ^ 2 -2x -15 = 0$$

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

$$r + s = 2 rs = -15$$

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

$$r = 1 - u s = 1 + u$$

To solve for unknown quantity u, substitute these in the product equation rs = -15

$$(1 - u) (1 + u) = -15$$

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

$$1 - u^2 = -15$$

Simplify the expression by subtracting 1 on both sides

$$-u^2 = -15-1 = -16$$

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

$$u^2 = 16 u = \pm\sqrt{16} = \pm 4$$

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

$$r =1 - 4 = -3 s = 1 + 4 = 5$$