Let {an} and {BN} which are all positive numbers satisfy the following conditions: 5 ^ an, 5 ^ BN, 5 ^ an + 1 is equal ratio sequence, lgbn, lgan + 1, lgbn + 1 is equal difference sequence, and A1 = 1, B1 = 2, A2 = 3. Guess an = n (n + 1) / 2 BN = (n + 1) * (n + 1) / 2 if we use mathematical induction, how to write when n = K + 1?

Let {an} and {BN} which are all positive numbers satisfy the following conditions: 5 ^ an, 5 ^ BN, 5 ^ an + 1 is equal ratio sequence, lgbn, lgan + 1, lgbn + 1 is equal difference sequence, and A1 = 1, B1 = 2, A2 = 3. Guess an = n (n + 1) / 2 BN = (n + 1) * (n + 1) / 2 if we use mathematical induction, how to write when n = K + 1?

Substitute a (K + 1) = (K + 1) (K + 2) / 2 B (K + 1) = (K + 2) ^ 2 / 2 into the known arithmetic sequence of arithmetic sequence to see if it is true