-7x^2+9x+28=8

Solution for -7x^2+9x+28=8 equation:

-7x^2+9x+28=8

We move all terms to the left:

-7x^2+9x+28-(8)=0

We add all the numbers together, and all the variables

-7x^2+9x+20=0

a = -7; b = 9; c = +20;
Δ = b2-4ac
Δ = 92-4·(-7)·20
Δ = 641
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(9)-\sqrt{641}}{2*-7}=\frac{-9-\sqrt{641}}{-14}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+\sqrt{641}}{2*-7}=\frac{-9+\sqrt{641}}{-14}
$