Solve g(x)=-2x^2+12x-20

$$g ( x ) = - 2 x ^ { 2 } + 12 x - 20$$

Factor

$$2\left(-x^{2}+6x-10\right)$$

Solution Steps

Factor out 2. Polynomial -x^{2}+6x-10 is not factored since it does not have any rational roots.

$$2\left(-x^{2}+6x-10\right)$$

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.

$$-2x^{2}+12x-20=0$$

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.

$$x=\frac{-12±\sqrt{12^{2}-4\left(-2\right)\left(-20\right)}}{2\left(-2\right)}$$

Square 12.

$$x=\frac{-12±\sqrt{144-4\left(-2\right)\left(-20\right)}}{2\left(-2\right)}$$

Multiply -4 times -2.

$$x=\frac{-12±\sqrt{144+8\left(-20\right)}}{2\left(-2\right)}$$

Multiply 8 times -20.

$$x=\frac{-12±\sqrt{144-160}}{2\left(-2\right)}$$

Add 144 to -160.

$$x=\frac{-12±\sqrt{-16}}{2\left(-2\right)}$$

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

$$-2x^{2}+12x-20$$

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.

$$x ^ 2 -6x +10 = 0$$

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

$$r + s = 6 rs = 10$$

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

$$r = 3 - u s = 3 + u$$

To solve for unknown quantity u, substitute these in the product equation rs = 10

$$(3 - u) (3 + u) = 10$$

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

$$9 - u^2 = 10$$

Simplify the expression by subtracting 9 on both sides

$$-u^2 = 10-9 = 1$$

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

$$u^2 = -1 u = \pm\sqrt{-1} = \pm i$$

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

$$r =3 - i s = 3 + i$$

Evaluate

$$-2x^{2}+12x-20$$