Solve 4a^2+16a-36

$$4 a ^ { 2 } + 16 a - 36$$

Factor

$$4\left(a-\left(-\sqrt{13}-2\right)\right)\left(a-\left(\sqrt{13}-2\right)\right)$$

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.

$$4a^{2}+16a-36=0$$

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.

$$a=\frac{-16±\sqrt{16^{2}-4\times 4\left(-36\right)}}{2\times 4}$$

Square 16.

$$a=\frac{-16±\sqrt{256-4\times 4\left(-36\right)}}{2\times 4}$$

Multiply -4 times 4.

$$a=\frac{-16±\sqrt{256-16\left(-36\right)}}{2\times 4}$$

Multiply -16 times -36.

$$a=\frac{-16±\sqrt{256+576}}{2\times 4}$$

Add 256 to 576.

$$a=\frac{-16±\sqrt{832}}{2\times 4}$$

Take the square root of 832.

$$a=\frac{-16±8\sqrt{13}}{2\times 4}$$

Multiply 2 times 4.

$$a=\frac{-16±8\sqrt{13}}{8}$$

Now solve the equation a=\frac{-16±8\sqrt{13}}{8} when ± is plus. Add -16 to 8\sqrt{13}.

$$a=\frac{8\sqrt{13}-16}{8}$$

Divide -16+8\sqrt{13} by 8.

$$a=\sqrt{13}-2$$

Now solve the equation a=\frac{-16±8\sqrt{13}}{8} when ± is minus. Subtract 8\sqrt{13} from -16.

$$a=\frac{-8\sqrt{13}-16}{8}$$

Divide -16-8\sqrt{13} by 8.

$$a=-\sqrt{13}-2$$

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

$$4a^{2}+16a-36=4\left(a-\left(\sqrt{13}-2\right)\right)\left(a-\left(-\sqrt{13}-2\right)\right)$$

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.This is achieved by dividing both sides of the equation by 4

$$x ^ 2 +4x -9 = 0$$

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

$$r + s = -4 rs = -9$$

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

$$r = -2 - u s = -2 + u$$

To solve for unknown quantity u, substitute these in the product equation rs = -9

$$(-2 - u) (-2 + u) = -9$$

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

$$4 - u^2 = -9$$

Simplify the expression by subtracting 4 on both sides

$$-u^2 = -9-4 = -13$$

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

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

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

$$r =-2 - \sqrt{13} = -5.606 s = -2 + \sqrt{13} = 1.606$$

Evaluate

$$4\left(a^{2}+4a-9\right)$$