PMI Proof Pre-Cal II (Help!)

Question

Using PMI, prove 1 + 1 +... + 1 = n-1 For n > 2

1*2 2*3 n(n-1) n

Answer 1

1/(1*2)+1/(2*3)+...+1/(n(n-1))=

=1/1-1/2+1/2-1/3+... +1/(n-2)-1/(n-1) +1(/n-1)-1/n)=

=1-1/n=(n-1)/n