4x(7x+2)=90

Solution for 4x(7x+2)=90 equation:

4x(7x+2)=90

We move all terms to the left:

4x(7x+2)-(90)=0

We multiply parentheses

28x^2+8x-90=0

a = 28; b = 8; c = -90;
Δ = b2-4ac
Δ = 82-4·28·(-90)
Δ = 10144
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:

$\sqrt{\Delta}=\sqrt{10144}=\sqrt{16*634}=\sqrt{16}*\sqrt{634}=4\sqrt{634}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(8)-4\sqrt{634}}{2*28}=\frac{-8-4\sqrt{634}}{56}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(8)+4\sqrt{634}}{2*28}=\frac{-8+4\sqrt{634}}{56}
$