factoring

"Competing the square" ->
n²+100 = n²+20n+100-20n = (n+10)²-20n

With (a-b)(a+b) = a² - b² ->
(n+10)² - sqrt(20n)² = (n+10)² - 20n
(n+10)² = a²
sqrt(20n)² = b²
=> (n+10+sqrt(20n))(n+10-sqrt(20n)) = n²+100

I meant completing, sorry :3