We can use the quadratic formula to solve this problem.
[tex]\sf x=\dfrac{-b\pm\sqrt{b^2-4ac}}{2a}[/tex]
You've already listed the values for 'a', 'b', and 'c', so just plug them into the formula:
[tex]\sf x=\dfrac{-(-12)\pm\sqrt{(-12)^2-4(4)(9)}}{2(4)}[/tex]
Simplify:
[tex]\sf x=\dfrac{12\pm\sqrt{144-4(4)(9)}}{8}[/tex]
Multiply:
[tex]\sf x=\dfrac{12\pm\sqrt{144-144}}{8}[/tex]
Subtract:
[tex]\sf x=\dfrac{12\pm\sqrt{0}}{8}[/tex]
Take the square root:
[tex]\sf x=\dfrac{12\pm 0}{8}[/tex]
It doesn't matter if you add or subtract something with 0, you'll end up with the same thing, so we have:
[tex]\sf x=\dfrac{12}{8}\rightarrow\boxed{\sf 1\dfrac{1}{2}}[/tex]
