A=x(x-13)

Solution for A=x(x-13) equation:

=A(A-13)

We move all terms to the left:

-(A(A-13))=0


We calculate terms in parentheses: -(A(A-13)), so:

A(A-13)

We multiply parentheses

A^2-13A

Back to the equation:

-(A^2-13A)


We get rid of parentheses

-A^2+13A=0

We add all the numbers together, and all the variables

-1A^2+13A=0

a = -1; b = 13; c = 0;
Δ = b2-4ac
Δ = 132-4·(-1)·0
Δ = 169
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{169}=13$
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(13)-13}{2*-1}=\frac{-26}{-2}
=+13
$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(13)+13}{2*-1}=\frac{0}{-2}
=0
$