-8x(5x+5)=7

Solution for -8x(5x+5)=7 equation:

-8x(5x+5)=7

We move all terms to the left:

-8x(5x+5)-(7)=0

We multiply parentheses

-40x^2-40x-7=0

a = -40; b = -40; c = -7;
Δ = b2-4ac
Δ = -402-4·(-40)·(-7)
Δ = 480
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{480}=\sqrt{16*30}=\sqrt{16}*\sqrt{30}=4\sqrt{30}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-40)-4\sqrt{30}}{2*-40}=\frac{40-4\sqrt{30}}{-80}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-40)+4\sqrt{30}}{2*-40}=\frac{40+4\sqrt{30}}{-80}
$