n(n+1)=45

Solution for n(n+1)=45 equation:

n(n+1)=45

We move all terms to the left:

n(n+1)-(45)=0

We multiply parentheses

n^2+n-45=0

a = 1; b = 1; c = -45;
Δ = b2-4ac
Δ = 12-4·1·(-45)
Δ = 181
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(1)-\sqrt{181}}{2*1}=\frac{-1-\sqrt{181}}{2}
$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{181}}{2*1}=\frac{-1+\sqrt{181}}{2}
$