340=n^2-3n

Solution for 340=n^2-3n equation:

340=n^2-3n

We move all terms to the left:

340-(n^2-3n)=0

We get rid of parentheses

-n^2+3n+340=0

We add all the numbers together, and all the variables

-1n^2+3n+340=0

a = -1; b = 3; c = +340;
Δ = b2-4ac
Δ = 32-4·(-1)·340
Δ = 1369
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1369}=37$
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(3)-37}{2*-1}=\frac{-40}{-2}
=+20
$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(3)+37}{2*-1}=\frac{34}{-2}
=-17
$