Solve -4m^2-8m+9

$$- 4 m ^ { 2 } - 8 m + 9$$

Factor

$$-4\left(m-\left(-\frac{\sqrt{13}}{2}-1\right)\right)\left(m-\left(\frac{\sqrt{13}}{2}-1\right)\right)$$

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.

$$-4m^{2}-8m+9=0$$

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.

$$m=\frac{-\left(-8\right)±\sqrt{\left(-8\right)^{2}-4\left(-4\right)\times 9}}{2\left(-4\right)}$$

Square -8.

$$m=\frac{-\left(-8\right)±\sqrt{64-4\left(-4\right)\times 9}}{2\left(-4\right)}$$

Multiply -4 times -4.

$$m=\frac{-\left(-8\right)±\sqrt{64+16\times 9}}{2\left(-4\right)}$$

Multiply 16 times 9.

$$m=\frac{-\left(-8\right)±\sqrt{64+144}}{2\left(-4\right)}$$

Add 64 to 144.

$$m=\frac{-\left(-8\right)±\sqrt{208}}{2\left(-4\right)}$$

Take the square root of 208.

$$m=\frac{-\left(-8\right)±4\sqrt{13}}{2\left(-4\right)}$$

The opposite of -8 is 8.

$$m=\frac{8±4\sqrt{13}}{2\left(-4\right)}$$

Multiply 2 times -4.

$$m=\frac{8±4\sqrt{13}}{-8}$$

Now solve the equation m=\frac{8±4\sqrt{13}}{-8} when ± is plus. Add 8 to 4\sqrt{13}.

$$m=\frac{4\sqrt{13}+8}{-8}$$

Divide 8+4\sqrt{13} by -8.

$$m=-\frac{\sqrt{13}}{2}-1$$

Now solve the equation m=\frac{8±4\sqrt{13}}{-8} when ± is minus. Subtract 4\sqrt{13} from 8.

$$m=\frac{8-4\sqrt{13}}{-8}$$

Divide 8-4\sqrt{13} by -8.

$$m=\frac{\sqrt{13}}{2}-1$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute -1-\frac{\sqrt{13}}{2} for x_{1} and -1+\frac{\sqrt{13}}{2} for x_{2}.

$$-4m^{2}-8m+9=-4\left(m-\left(-\frac{\sqrt{13}}{2}-1\right)\right)\left(m-\left(\frac{\sqrt{13}}{2}-1\right)\right)$$

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.

$$x ^ 2 +2x -\frac{9}{4} = 0$$

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

$$r + s = -2 rs = -\frac{9}{4}$$

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-gzdabgg4ehffg0hf.b01.azurefd.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 = -\frac{9}{4}

$$(-1 - u) (-1 + u) = -\frac{9}{4}$$

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

$$1 - u^2 = -\frac{9}{4}$$

Simplify the expression by subtracting 1 on both sides

$$-u^2 = -\frac{9}{4}-1 = -\frac{13}{4}$$

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

$$u^2 = \frac{13}{4} u = \pm\sqrt{\frac{13}{4}} = \pm \frac{\sqrt{13}}{2}$$

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

$$r =-1 - \frac{\sqrt{13}}{2} = -2.803 s = -1 + \frac{\sqrt{13}}{2} = 0.803$$

Evaluate

$$9-8m-4m^{2}$$