Solve 5x^2+17x+5

$$5 x ^ { 2 } + 17 x + 5$$

Factor

$$5\left(x-\frac{-3\sqrt{21}-17}{10}\right)\left(x-\frac{3\sqrt{21}-17}{10}\right)$$

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.

$$5x^{2}+17x+5=0$$

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.

$$x=\frac{-17±\sqrt{17^{2}-4\times 5\times 5}}{2\times 5}$$

Square 17.

$$x=\frac{-17±\sqrt{289-4\times 5\times 5}}{2\times 5}$$

Multiply -4 times 5.

$$x=\frac{-17±\sqrt{289-20\times 5}}{2\times 5}$$

Multiply -20 times 5.

$$x=\frac{-17±\sqrt{289-100}}{2\times 5}$$

Add 289 to -100.

$$x=\frac{-17±\sqrt{189}}{2\times 5}$$

Take the square root of 189.

$$x=\frac{-17±3\sqrt{21}}{2\times 5}$$

Multiply 2 times 5.

$$x=\frac{-17±3\sqrt{21}}{10}$$

Now solve the equation x=\frac{-17±3\sqrt{21}}{10} when ± is plus. Add -17 to 3\sqrt{21}.

$$x=\frac{3\sqrt{21}-17}{10}$$

Now solve the equation x=\frac{-17±3\sqrt{21}}{10} when ± is minus. Subtract 3\sqrt{21} from -17.

$$x=\frac{-3\sqrt{21}-17}{10}$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute \frac{-17+3\sqrt{21}}{10} for x_{1} and \frac{-17-3\sqrt{21}}{10} for x_{2}.

$$5x^{2}+17x+5=5\left(x-\frac{3\sqrt{21}-17}{10}\right)\left(x-\frac{-3\sqrt{21}-17}{10}\right)$$

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 5

$$x ^ 2 +\frac{17}{5}x +1 = 0$$

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

$$r + s = -\frac{17}{5} rs = 1$$

Two numbers r and s sum up to -\frac{17}{5} exactly when the average of the two numbers is \frac{1}{2}*-\frac{17}{5} = -\frac{17}{10}. 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>

$$r = -\frac{17}{10} - u s = -\frac{17}{10} + u$$

To solve for unknown quantity u, substitute these in the product equation rs = 1

$$(-\frac{17}{10} - u) (-\frac{17}{10} + u) = 1$$

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

$$\frac{289}{100} - u^2 = 1$$

Simplify the expression by subtracting \frac{289}{100} on both sides

$$-u^2 = 1-\frac{289}{100} = -\frac{189}{100}$$

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

$$u^2 = \frac{189}{100} u = \pm\sqrt{\frac{189}{100}} = \pm \frac{\sqrt{189}}{10}$$

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

$$r =-\frac{17}{10} - \frac{\sqrt{189}}{10} = -3.075 s = -\frac{17}{10} + \frac{\sqrt{189}}{10} = -0.325$$

Evaluate

$$5x^{2}+17x+5$$