70=x^2+3x

Solution for 70=x^2+3x equation:

70=x^2+3x

We move all terms to the left:

70-(x^2+3x)=0

We get rid of parentheses

-x^2-3x+70=0

We add all the numbers together, and all the variables

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