2x^2-11x-21=7

Solution for 2x^2-11x-21=7 equation:

2x^2-11x-21=7

We move all terms to the left:

2x^2-11x-21-(7)=0

We add all the numbers together, and all the variables

2x^2-11x-28=0

a = 2; b = -11; c = -28;
Δ = b2-4ac
Δ = -112-4·2·(-28)
Δ = 345
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{-(-11)-\sqrt{345}}{2*2}=\frac{11-\sqrt{345}}{4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-11)+\sqrt{345}}{2*2}=\frac{11+\sqrt{345}}{4}
$