Use induction to prove that 1-3+9...+(-3)" - 1-(-3)+1 = 4 #1 AZ Use induction to prove that n-1(r + 1) (r +2) = a n(n+1) (n + 2) (n + 3) #3 3 Use induction to prove n3 + 2n is divisible by 3 for all integers n