(6-y)(-y-13)=0

Solution for (6-y)(-y-13)=0 equation:

(6-y)(-y-13)=0

We add all the numbers together, and all the variables

(-1y+6)(-1y-13)=0

We multiply parentheses ..

(+y^2+13y-6y-78)=0

We get rid of parentheses

y^2+13y-6y-78=0

We add all the numbers together, and all the variables

y^2+7y-78=0

a = 1; b = 7; c = -78;
Δ = b2-4ac
Δ = 72-4·1·(-78)
Δ = 361
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{361}=19$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(7)-19}{2*1}=\frac{-26}{2}
=-13
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(7)+19}{2*1}=\frac{12}{2}
=6
$