Solve -2k^2-16k+12

$$- 2 k ^ { 2 } - 16 k + 12$$

Factor

$$-2\left(k-\left(-\sqrt{22}-4\right)\right)\left(k-\left(\sqrt{22}-4\right)\right)$$

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.

$$-2k^{2}-16k+12=0$$

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.

$$k=\frac{-\left(-16\right)±\sqrt{\left(-16\right)^{2}-4\left(-2\right)\times 12}}{2\left(-2\right)}$$

Square -16.

$$k=\frac{-\left(-16\right)±\sqrt{256-4\left(-2\right)\times 12}}{2\left(-2\right)}$$

Multiply -4 times -2.

$$k=\frac{-\left(-16\right)±\sqrt{256+8\times 12}}{2\left(-2\right)}$$

Multiply 8 times 12.

$$k=\frac{-\left(-16\right)±\sqrt{256+96}}{2\left(-2\right)}$$

Add 256 to 96.

$$k=\frac{-\left(-16\right)±\sqrt{352}}{2\left(-2\right)}$$

Take the square root of 352.

$$k=\frac{-\left(-16\right)±4\sqrt{22}}{2\left(-2\right)}$$

The opposite of -16 is 16.

$$k=\frac{16±4\sqrt{22}}{2\left(-2\right)}$$

Multiply 2 times -2.

$$k=\frac{16±4\sqrt{22}}{-4}$$

Now solve the equation k=\frac{16±4\sqrt{22}}{-4} when ± is plus. Add 16 to 4\sqrt{22}.

$$k=\frac{4\sqrt{22}+16}{-4}$$

Divide 16+4\sqrt{22} by -4.

$$k=-\left(\sqrt{22}+4\right)$$

Now solve the equation k=\frac{16±4\sqrt{22}}{-4} when ± is minus. Subtract 4\sqrt{22} from 16.

$$k=\frac{16-4\sqrt{22}}{-4}$$

Divide 16-4\sqrt{22} by -4.

$$k=\sqrt{22}-4$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute -\left(4+\sqrt{22}\right) for x_{1} and -4+\sqrt{22} for x_{2}.

$$-2k^{2}-16k+12=-2\left(k-\left(-\left(\sqrt{22}+4\right)\right)\right)\left(k-\left(\sqrt{22}-4\right)\right)$$

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.

$$x ^ 2 +8x -6 = 0$$

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

$$r + s = -8 rs = -6$$

Two numbers r and s sum up to -8 exactly when the average of the two numbers is \frac{1}{2}*-8 = -4. 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>

$$r = -4 - u s = -4 + u$$

To solve for unknown quantity u, substitute these in the product equation rs = -6

$$(-4 - u) (-4 + u) = -6$$

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

$$16 - u^2 = -6$$

Simplify the expression by subtracting 16 on both sides

$$-u^2 = -6-16 = -22$$

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

$$u^2 = 22 u = \pm\sqrt{22} = \pm \sqrt{22}$$

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

$$r =-4 - \sqrt{22} = -8.690 s = -4 + \sqrt{22} = 0.690$$

Evaluate

$$12-16k-2k^{2}$$