a=a*a-30

Solution for a=a*a-30 equation:

a=a*a-30

We move all terms to the left:

a-(a*a-30)=0

We get rid of parentheses

a-a*a+30=0

Wy multiply elements

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