a(a-1)=3(2+1)-3

Solution for a(a-1)=3(2+1)-3 equation:

a(a-1)=3(2+1)-3

We move all terms to the left:

a(a-1)-(3(2+1)-3)=0

We add all the numbers together, and all the variables

a(a-1)-(33-3)=0

We add all the numbers together, and all the variables

a(a-1)-30=0

We multiply parentheses

a^2-1a-30=0

a = 1; b = -1; c = -30;
Δ = b2-4ac
Δ = -12-4·1·(-30)
Δ = 121
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{121}=11$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-11}{2*1}=\frac{-10}{2}
=-5
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+11}{2*1}=\frac{12}{2}
=6
$