"Subtract b²:          a² - b² = ab - b²"

"Evaluated" is         0 = 0

The subsequent division is a "divide by zero."

Any fool knows that zero divided by zero can have any answer you want, depending on whether the bigger zero is on the top or on the bottom.



(n-1)*a = n*a – a = 0

for n = 1

(n – 1) = 1 – 1 = 0

(1 – 1) * a = a – a = 0

For the same reason that 0! = 1 and not 0.

Clear?

John