To solve the equation, factor the left hand side by grouping. First, left hand side needs to be rewritten as $4x^{2}+ax+bx+25$. To find $a$ and $b$, set up a system to be solved.
$$a+b=20$$ $$ab=4\times 25=100$$
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 $100$.
Rewrite $4x^{2}+20x+25$ as $\left(4x^{2}+10x\right)+\left(10x+25\right)$.
$$\left(4x^{2}+10x\right)+\left(10x+25\right)$$
Factor out $2x$ in the first and $5$ in the second group.
$$2x\left(2x+5\right)+5\left(2x+5\right)$$
Factor out common term $2x+5$ by using distributive property.
$$\left(2x+5\right)\left(2x+5\right)$$
Rewrite as a binomial square.
$$\left(2x+5\right)^{2}$$
To find equation solution, solve $2x+5=0$.
$$x=-\frac{5}{2}$$
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.
This equation is in standard form: $ax^{2}+bx+c=0$. Substitute $4$ for $a$, $20$ for $b$, and $25$ for $c$ in the quadratic formula, $\frac{-b±\sqrt{b^{2}-4ac}}{2a}$.
Reduce the fraction $\frac{-20}{8}$ to lowest terms by extracting and canceling out $4$.
$$x=-\frac{5}{2}$$
Steps for Completing the Square
Quadratic equations such as this one can be solved by completing the square. In order to complete the square, the equation must first be in the form $x^{2}+bx=c$.
$$4x^{2}+20x=-25$$
Divide both sides by $4$.
$$\frac{4x^{2}+20x}{4}=-\frac{25}{4}$$
Dividing by $4$ undoes the multiplication by $4$.
$$x^{2}+\frac{20}{4}x=-\frac{25}{4}$$
Divide $20$ by $4$.
$$x^{2}+5x=-\frac{25}{4}$$
Divide $5$, the coefficient of the $x$ term, by $2$ to get $\frac{5}{2}$. Then add the square of $\frac{5}{2}$ to both sides of the equation. This step makes the left hand side of the equation a perfect square.
