Solve 5y^2+17y+14

$$5 y ^ { 2 } + 17 y + 14$$

Factor

$$\left(y+2\right)\left(5y+7\right)$$

Solution Steps

Factor the expression by grouping. First, the expression needs to be rewritten as 5y^{2}+ay+by+14. To find a and b, set up a system to be solved.

$$a+b=17 ab=5\times 14=70$$

Since ab is positive, a and b have the same sign. Since a+b is positive, a and b are both positive. List all such integer pairs that give product 70.

$$1,70 2,35 5,14 7,10$$

Calculate the sum for each pair.

$$1+70=71 2+35=37 5+14=19 7+10=17$$

The solution is the pair that gives sum 17.

$$a=7 b=10$$

Rewrite 5y^{2}+17y+14 as \left(5y^{2}+7y\right)+\left(10y+14\right).

$$\left(5y^{2}+7y\right)+\left(10y+14\right)$$

Factor out y in the first and 2 in the second group.

$$y\left(5y+7\right)+2\left(5y+7\right)$$

Factor out common term 5y+7 by using distributive property.

$$\left(5y+7\right)\left(y+2\right)$$

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.

$$5y^{2}+17y+14=0$$

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.

$$y=\frac{-17±\sqrt{17^{2}-4\times 5\times 14}}{2\times 5}$$

Square 17.

$$y=\frac{-17±\sqrt{289-4\times 5\times 14}}{2\times 5}$$

Multiply -4 times 5.

$$y=\frac{-17±\sqrt{289-20\times 14}}{2\times 5}$$

Multiply -20 times 14.

$$y=\frac{-17±\sqrt{289-280}}{2\times 5}$$

Add 289 to -280.

$$y=\frac{-17±\sqrt{9}}{2\times 5}$$

Take the square root of 9.

$$y=\frac{-17±3}{2\times 5}$$

Multiply 2 times 5.

$$y=\frac{-17±3}{10}$$

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

$$y=-\frac{14}{10}$$

Reduce the fraction \frac{-14}{10} to lowest terms by extracting and canceling out 2.

$$y=-\frac{7}{5}$$

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

$$y=-\frac{20}{10}$$

Divide -20 by 10.

$$y=-2$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute -\frac{7}{5} for x_{1} and -2 for x_{2}.

$$5y^{2}+17y+14=5\left(y-\left(-\frac{7}{5}\right)\right)\left(y-\left(-2\right)\right)$$

Simplify all the expressions of the form p-\left(-q\right) to p+q.

$$5y^{2}+17y+14=5\left(y+\frac{7}{5}\right)\left(y+2\right)$$

Add \frac{7}{5} to y by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$5y^{2}+17y+14=5\times \frac{5y+7}{5}\left(y+2\right)$$

Cancel out 5, the greatest common factor in 5 and 5.

$$5y^{2}+17y+14=\left(5y+7\right)\left(y+2\right)$$

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

$$x ^ 2 +\frac{17}{5}x +\frac{14}{5} = 0$$

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

$$r + s = -\frac{17}{5} rs = \frac{14}{5}$$

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 = \frac{14}{5}

$$(-\frac{17}{10} - u) (-\frac{17}{10} + u) = \frac{14}{5}$$

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

$$\frac{289}{100} - u^2 = \frac{14}{5}$$

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

$$-u^2 = \frac{14}{5}-\frac{289}{100} = -\frac{9}{100}$$

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

$$u^2 = \frac{9}{100} u = \pm\sqrt{\frac{9}{100}} = \pm \frac{3}{10}$$

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

$$r =-\frac{17}{10} - \frac{3}{10} = -2.000 s = -\frac{17}{10} + \frac{3}{10} = -1.400$$

Evaluate

$$\left(y+2\right)\left(5y+7\right)$$