Question

solve n(n-1)/2 = 28
step by step

Answer 1

n(n-1)=56
n^2-n=56

n^2 - n -56==0
n^2 - 8n + 7n - 56==0
n (n-8) + 7(n-8) ==0
(n-8) (n+7)==0
n == 8 or -7

Answer 2

pls see the attachment above