(7x+2x)x=85

Solution for (7x+2x)x=85 equation:

(7x+2x)x=85

We move all terms to the left:

(7x+2x)x-(85)=0

We add all the numbers together, and all the variables

(+9x)x-85=0

We multiply parentheses

9x^2-85=0

a = 9; b = 0; c = -85;
Δ = b2-4ac
Δ = 02-4·9·(-85)
Δ = 3060
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:

$\sqrt{\Delta}=\sqrt{3060}=\sqrt{36*85}=\sqrt{36}*\sqrt{85}=6\sqrt{85}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-6\sqrt{85}}{2*9}=\frac{0-6\sqrt{85}}{18}
=-\frac{6\sqrt{85}}{18}
=-\frac{\sqrt{85}}{3}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+6\sqrt{85}}{2*9}=\frac{0+6\sqrt{85}}{18}
=\frac{6\sqrt{85}}{18}
=\frac{\sqrt{85}}{3}
$