5(5x+5)x-5=15

Solution for 5(5x+5)x-5=15 equation:

5(5x+5)x-5=15

We move all terms to the left:

5(5x+5)x-5-(15)=0

We add all the numbers together, and all the variables

5(5x+5)x-20=0

We multiply parentheses

25x^2+25x-20=0

a = 25; b = 25; c = -20;
Δ = b2-4ac
Δ = 252-4·25·(-20)
Δ = 2625
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:

$\sqrt{\Delta}=\sqrt{2625}=\sqrt{25*105}=\sqrt{25}*\sqrt{105}=5\sqrt{105}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(25)-5\sqrt{105}}{2*25}=\frac{-25-5\sqrt{105}}{50}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(25)+5\sqrt{105}}{2*25}=\frac{-25+5\sqrt{105}}{50}
$