m(m-1)=210

Solution for m(m-1)=210 equation:

m(m-1)=210

We move all terms to the left:

m(m-1)-(210)=0

We multiply parentheses

m^2-1m-210=0

a = 1; b = -1; c = -210;
Δ = b2-4ac
Δ = -12-4·1·(-210)
Δ = 841
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$m_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$m_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{841}=29$
$m_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-29}{2*1}=\frac{-28}{2}
=-14
$
$m_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+29}{2*1}=\frac{30}{2}
=15
$