-13a+(a.2)*(a-1)=-18

Solution for -13a+(a.2)*(a-1)=-18 equation:

-13a+(a.2)(a-1)=-18

We move all terms to the left:

-13a+(a.2)(a-1)-(-18)=0

We add all the numbers together, and all the variables

-13a+(+a.2)(a-1)-(-18)=0

We add all the numbers together, and all the variables

-13a+(+a.2)(a-1)+18=0

We multiply parentheses ..

(+a^2-1a)-13a+18=0

We get rid of parentheses

a^2-1a-13a+18=0

We add all the numbers together, and all the variables

a^2-14a+18=0

a = 1; b = -14; c = +18;
Δ = b2-4ac
Δ = -142-4·1·18
Δ = 124
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{124}=\sqrt{4*31}=\sqrt{4}*\sqrt{31}=2\sqrt{31}$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-14)-2\sqrt{31}}{2*1}=\frac{14-2\sqrt{31}}{2}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-14)+2\sqrt{31}}{2*1}=\frac{14+2\sqrt{31}}{2}
$