To solve the equation, factor the left hand side by grouping. First, left hand side needs to be rewritten as $9x^{2}+ax+bx+4$. To find $a$ and $b$, set up a system to be solved.
$$a+b=12$$ $$ab=9\times 4=36$$
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 $36$.
Rewrite $9x^{2}+12x+4$ as $\left(9x^{2}+6x\right)+\left(6x+4\right)$.
$$\left(9x^{2}+6x\right)+\left(6x+4\right)$$
Factor out $3x$ in the first and $2$ in the second group.
$$3x\left(3x+2\right)+2\left(3x+2\right)$$
Factor out common term $3x+2$ by using distributive property.
$$\left(3x+2\right)\left(3x+2\right)$$
Rewrite as a binomial square.
$$\left(3x+2\right)^{2}$$
To find equation solution, solve $3x+2=0$.
$$x=-\frac{2}{3}$$
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.
$$9x^{2}+12x+4=0$$
This equation is in standard form: $ax^{2}+bx+c=0$. Substitute $9$ for $a$, $12$ for $b$, and $4$ for $c$ in the quadratic formula, $\frac{-b±\sqrt{b^{2}-4ac}}{2a}$.
Reduce the fraction $\frac{-12}{18}$ to lowest terms by extracting and canceling out $6$.
$$x=-\frac{2}{3}$$
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 $x^{2}+bx=c$.
$$9x^{2}+12x+4=0$$
Subtract $4$ from both sides of the equation.
$$9x^{2}+12x+4-4=-4$$
Subtracting $4$ from itself leaves $0$.
$$9x^{2}+12x=-4$$
Divide both sides by $9$.
$$\frac{9x^{2}+12x}{9}=-\frac{4}{9}$$
Dividing by $9$ undoes the multiplication by $9$.
$$x^{2}+\frac{12}{9}x=-\frac{4}{9}$$
Reduce the fraction $\frac{12}{9}$ to lowest terms by extracting and canceling out $3$.
$$x^{2}+\frac{4}{3}x=-\frac{4}{9}$$
Divide $\frac{4}{3}$, the coefficient of the $x$ term, by $2$ to get $\frac{2}{3}$. Then add the square of $\frac{2}{3}$ to both sides of the equation. This step makes the left hand side of the equation a perfect square.
Square $\frac{2}{3}$ by squaring both the numerator and the denominator of the fraction.
$$x^{2}+\frac{4}{3}x+\frac{4}{9}=\frac{-4+4}{9}$$
Add $-\frac{4}{9}$ to $\frac{4}{9}$ by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.
$$x^{2}+\frac{4}{3}x+\frac{4}{9}=0$$
Factor $x^{2}+\frac{4}{3}x+\frac{4}{9}$. In general, when $x^{2}+bx+c$ is a perfect square, it can always be factored as $\left(x+\frac{b}{2}\right)^{2}$.
$$\left(x+\frac{2}{3}\right)^{2}=0$$
Take the square root of both sides of the equation.
Subtract $\frac{2}{3}$ from both sides of the equation.
$$x=-\frac{2}{3}$$ $$x=-\frac{2}{3}$$
The equation is now solved. Solutions are the same.
$$x=-\frac{2}{3}$$
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 $9$
$$x ^ 2 +\frac{4}{3}x +\frac{4}{9} = 0$$
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 $rs = C$
$$r + s = -\frac{4}{3} $$ $$ rs = \frac{4}{9}$$
Two numbers $r$ and $s$ sum up to $-\frac{4}{3}$ exactly when the average of the two numbers is $\frac{1}{2}*-\frac{4}{3} = -\frac{2}{3}$. 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 $u$.
$$r = -\frac{2}{3} - u$$ $$s = -\frac{2}{3} + u$$
To solve for unknown quantity $u$, substitute these in the product equation $rs = \frac{4}{9}$
