You must have a typo
in 3+4+5+ ... + (n+2)
the general term does not match your first three numbers
Prove 3+4+5+...+(n+2) = [n(n+5)]/2 for n>4
Do the first step in a proof by induction.
2 answers
I'm not sure. It was on my math test. I typed it out exactly like it said on the test.