4x^2+15x=90

Solution for 4x^2+15x=90 equation:

4x^2+15x=90

We move all terms to the left:

4x^2+15x-(90)=0

a = 4; b = 15; c = -90;
Δ = b2-4ac
Δ = 152-4·4·(-90)
Δ = 1665
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:

$\sqrt{\Delta}=\sqrt{1665}=\sqrt{9*185}=\sqrt{9}*\sqrt{185}=3\sqrt{185}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-3\sqrt{185}}{2*4}=\frac{-15-3\sqrt{185}}{8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+3\sqrt{185}}{2*4}=\frac{-15+3\sqrt{185}}{8}
$