Solve x^2+5x+25/4=81/4

$$x ^ { 2 } + 5 x + \frac { 25 } { 4 } = \frac { 81 } { 4 }$$

Solve for x

$$x=-7$$

$$x=2$$

Steps Using Factoring

Subtract \frac{81}{4} from both sides.

$$x^{2}+5x+\frac{25}{4}-\frac{81}{4}=0$$

Subtract \frac{81}{4} from \frac{25}{4} to get -14.

$$x^{2}+5x-14=0$$

To solve the equation, factor x^{2}+5x-14 using formula x^{2}+\left(a+b\right)x+ab=\left(x+a\right)\left(x+b\right). To find a and b, set up a system to be solved.

$$a+b=5 ab=-14$$

Since ab is negative, a and b have the opposite signs. Since a+b is positive, the positive number has greater absolute value than the negative. List all such integer pairs that give product -14.

$$-1,14 -2,7$$

Calculate the sum for each pair.

$$-1+14=13 -2+7=5$$

The solution is the pair that gives sum 5.

$$a=-2 b=7$$

Rewrite factored expression \left(x+a\right)\left(x+b\right) using the obtained values.

$$\left(x-2\right)\left(x+7\right)$$

To find equation solutions, solve x-2=0 and x+7=0.

$$x=2 x=-7$$

Steps Using Factoring By Grouping

Subtract \frac{81}{4} from both sides.

$$x^{2}+5x+\frac{25}{4}-\frac{81}{4}=0$$

Subtract \frac{81}{4} from \frac{25}{4} to get -14.

$$x^{2}+5x-14=0$$

To solve the equation, factor the left hand side by grouping. First, left hand side needs to be rewritten as x^{2}+ax+bx-14. To find a and b, set up a system to be solved.

$$a+b=5 ab=1\left(-14\right)=-14$$

Since ab is negative, a and b have the opposite signs. Since a+b is positive, the positive number has greater absolute value than the negative. List all such integer pairs that give product -14.

$$-1,14 -2,7$$

Calculate the sum for each pair.

$$-1+14=13 -2+7=5$$

The solution is the pair that gives sum 5.

$$a=-2 b=7$$

Rewrite x^{2}+5x-14 as \left(x^{2}-2x\right)+\left(7x-14\right).

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

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

$$x\left(x-2\right)+7\left(x-2\right)$$

Factor out common term x-2 by using distributive property.

$$\left(x-2\right)\left(x+7\right)$$

To find equation solutions, solve x-2=0 and x+7=0.

$$x=2 x=-7$$

Steps Using the Quadratic Formula

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.

$$x^{2}+5x+\frac{25}{4}=\frac{81}{4}$$

Subtract \frac{81}{4} from both sides of the equation.

$$x^{2}+5x+\frac{25}{4}-\frac{81}{4}=\frac{81}{4}-\frac{81}{4}$$

Subtracting \frac{81}{4} from itself leaves 0.

$$x^{2}+5x+\frac{25}{4}-\frac{81}{4}=0$$

Subtract \frac{81}{4} from \frac{25}{4} by finding a common denominator and subtracting the numerators. Then reduce the fraction to lowest terms if possible.

$$x^{2}+5x-14=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 1 for a, 5 for b, and -14 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-5±\sqrt{5^{2}-4\left(-14\right)}}{2}$$

Square 5.

$$x=\frac{-5±\sqrt{25-4\left(-14\right)}}{2}$$

Multiply -4 times -14.

$$x=\frac{-5±\sqrt{25+56}}{2}$$

Add 25 to 56.

$$x=\frac{-5±\sqrt{81}}{2}$$

Take the square root of 81.

$$x=\frac{-5±9}{2}$$

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

$$x=\frac{4}{2}$$

Divide 4 by 2.

$$x=2$$

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

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

Divide -14 by 2.

$$x=-7$$

The equation is now solved.

$$x=2 x=-7$$

Steps for Completing the Square

Factor x^{2}+5x+\frac{25}{4}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(x+\frac{5}{2}\right)^{2}=\frac{81}{4}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x+\frac{5}{2}\right)^{2}}=\sqrt{\frac{81}{4}}$$

Simplify.

$$x+\frac{5}{2}=\frac{9}{2} x+\frac{5}{2}=-\frac{9}{2}$$

Subtract \frac{5}{2} from both sides of the equation.

$$x=2 x=-7$$