Answer
x=-6, $\frac{14}{5}$
Work Step by Step
The quadratic formula states that if a$x^{2}$+bx+c=0, and a$\ne$0, then
$x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}$. If
5$x^{2}$+16x-84=0, then a=5, b=16, and c=-84, and to solve for x, then all we must do is plug the numbers into the quadratic formula then simplify.
$x=\frac{-16\pm\sqrt{(16)^2-4(5)(-84)}}{2(5)}$
=$\frac{-16\pm\sqrt{256-(-1680)}}{10}$ (16 squared=256, 4*5*-84=-1680, and 2*5=10)
=$\frac{-16\pm\sqrt{1936}}{10}$ (256-(-1680)=1936)
=$\frac{-16\pm44}{10}$ (The square root of 1936=44)
Since there is a plus minus symbol, we of course need to make sure that we compute both of our answers.
x=$\frac{-16+44}{10}$=$\frac{28}{10}$=$\frac{14}{5}$
x=$\frac{-16-44}{10}$=$\frac{-60}{10}$=-6
