Solve p^2+9p+14

$$p ^ { 2 } + 9 p + 14$$

Factor

$$\left(p+2\right)\left(p+7\right)$$

Solution Steps

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

$$a+b=9 ab=1\times 14=14$$

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 14.

$$1,14 2,7$$

Calculate the sum for each pair.

$$1+14=15 2+7=9$$

The solution is the pair that gives sum 9.

$$a=2 b=7$$

Rewrite p^{2}+9p+14 as \left(p^{2}+2p\right)+\left(7p+14\right).

$$\left(p^{2}+2p\right)+\left(7p+14\right)$$

Factor out p in the first and 7 in the second group.

$$p\left(p+2\right)+7\left(p+2\right)$$

Factor out common term p+2 by using distributive property.

$$\left(p+2\right)\left(p+7\right)$$

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.

$$p^{2}+9p+14=0$$

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.

$$p=\frac{-9±\sqrt{9^{2}-4\times 14}}{2}$$

Square 9.

$$p=\frac{-9±\sqrt{81-4\times 14}}{2}$$

Multiply -4 times 14.

$$p=\frac{-9±\sqrt{81-56}}{2}$$

Add 81 to -56.

$$p=\frac{-9±\sqrt{25}}{2}$$

Take the square root of 25.

$$p=\frac{-9±5}{2}$$

Now solve the equation p=\frac{-9±5}{2} when ± is plus. Add -9 to 5.

$$p=-\frac{4}{2}$$

Divide -4 by 2.

$$p=-2$$

Now solve the equation p=\frac{-9±5}{2} when ± is minus. Subtract 5 from -9.

$$p=-\frac{14}{2}$$

Divide -14 by 2.

$$p=-7$$

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

$$p^{2}+9p+14=\left(p-\left(-2\right)\right)\left(p-\left(-7\right)\right)$$

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

$$p^{2}+9p+14=\left(p+2\right)\left(p+7\right)$$

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.

$$x ^ 2 +9x +14 = 0$$

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

$$r + s = -9 rs = 14$$

Two numbers r and s sum up to -9 exactly when the average of the two numbers is \frac{1}{2}*-9 = -\frac{9}{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>

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

To solve for unknown quantity u, substitute these in the product equation rs = 14

$$(-\frac{9}{2} - u) (-\frac{9}{2} + u) = 14$$

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

$$\frac{81}{4} - u^2 = 14$$

Simplify the expression by subtracting \frac{81}{4} on both sides

$$-u^2 = 14-\frac{81}{4} = -\frac{25}{4}$$

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

$$u^2 = \frac{25}{4} u = \pm\sqrt{\frac{25}{4}} = \pm \frac{5}{2}$$

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

$$r =-\frac{9}{2} - \frac{5}{2} = -7 s = -\frac{9}{2} + \frac{5}{2} = -2$$

Evaluate

$$\left(p+2\right)\left(p+7\right)$$