4(-5x+7)5x=15

Solution for 4(-5x+7)5x=15 equation:

4(-5x+7)5x=15

We move all terms to the left:

4(-5x+7)5x-(15)=0

We multiply parentheses

-100x^2+140x-15=0

a = -100; b = 140; c = -15;
Δ = b2-4ac
Δ = 1402-4·(-100)·(-15)
Δ = 13600
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:

$\sqrt{\Delta}=\sqrt{13600}=\sqrt{400*34}=\sqrt{400}*\sqrt{34}=20\sqrt{34}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(140)-20\sqrt{34}}{2*-100}=\frac{-140-20\sqrt{34}}{-200}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(140)+20\sqrt{34}}{2*-100}=\frac{-140+20\sqrt{34}}{-200}
$