Solve a^2+4a-54

$$a ^ { 2 } + 4 a - 54$$

Factor

$$\left(a-\left(-\sqrt{58}-2\right)\right)\left(a-\left(\sqrt{58}-2\right)\right)$$

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.

$$a^{2}+4a-54=0$$

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.

$$a=\frac{-4±\sqrt{4^{2}-4\left(-54\right)}}{2}$$

Square 4.

$$a=\frac{-4±\sqrt{16-4\left(-54\right)}}{2}$$

Multiply -4 times -54.

$$a=\frac{-4±\sqrt{16+216}}{2}$$

Add 16 to 216.

$$a=\frac{-4±\sqrt{232}}{2}$$

Take the square root of 232.

$$a=\frac{-4±2\sqrt{58}}{2}$$

Now solve the equation a=\frac{-4±2\sqrt{58}}{2} when ± is plus. Add -4 to 2\sqrt{58}.

$$a=\frac{2\sqrt{58}-4}{2}$$

Divide -4+2\sqrt{58} by 2.

$$a=\sqrt{58}-2$$

Now solve the equation a=\frac{-4±2\sqrt{58}}{2} when ± is minus. Subtract 2\sqrt{58} from -4.

$$a=\frac{-2\sqrt{58}-4}{2}$$

Divide -4-2\sqrt{58} by 2.

$$a=-\sqrt{58}-2$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute -2+\sqrt{58} for x_{1} and -2-\sqrt{58} for x_{2}.

$$a^{2}+4a-54=\left(a-\left(\sqrt{58}-2\right)\right)\left(a-\left(-\sqrt{58}-2\right)\right)$$

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.

$$x ^ 2 +4x -54 = 0$$

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

$$r + s = -4 rs = -54$$

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 = -54

$$(-2 - u) (-2 + u) = -54$$

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

$$4 - u^2 = -54$$

Simplify the expression by subtracting 4 on both sides

$$-u^2 = -54-4 = -58$$

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

$$u^2 = 58 u = \pm\sqrt{58} = \pm \sqrt{58}$$

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

$$r =-2 - \sqrt{58} = -9.616 s = -2 + \sqrt{58} = 5.616$$

Evaluate

$$a^{2}+4a-54$$