It goes +6 +8 +10 so the second differance is 2 you half the second difference to get n^2 You write out the values for n^2 1 4 9 16 Compare with first sequence 6 12 20 30 The difference between these two is +5 +8 +11 and you see this is linear now you solve this to get 3n+2 You add the n^2 to get n^2+3n+2
