x*x+3*x=70

Solution for x*x+3*x=70 equation:

x*x+3x=70

We move all terms to the left:

x*x+3x-(70)=0

We add all the numbers together, and all the variables

3x+x*x-70=0

Wy multiply elements

x^2+3x-70=0

a = 1; b = 3; c = -70;
Δ = b2-4ac
Δ = 32-4·1·(-70)
Δ = 289
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{289}=17$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(3)-17}{2*1}=\frac{-20}{2}
=-10
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(3)+17}{2*1}=\frac{14}{2}
=7
$