90=3x(5x+2)

Solution for 90=3x(5x+2) equation:

90=3x(5x+2)

We move all terms to the left:

90-(3x(5x+2))=0


We calculate terms in parentheses: -(3x(5x+2)), so:

3x(5x+2)

We multiply parentheses

15x^2+6x

Back to the equation:

-(15x^2+6x)


We get rid of parentheses

-15x^2-6x+90=0

a = -15; b = -6; c = +90;
Δ = b2-4ac
Δ = -62-4·(-15)·90
Δ = 5436
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:

$\sqrt{\Delta}=\sqrt{5436}=\sqrt{36*151}=\sqrt{36}*\sqrt{151}=6\sqrt{151}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-6)-6\sqrt{151}}{2*-15}=\frac{6-6\sqrt{151}}{-30}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-6)+6\sqrt{151}}{2*-15}=\frac{6+6\sqrt{151}}{-30}
$