If M-N = 3, Mn = 10, then m to the second power + n to the second power= Explain why

If M-N = 3, Mn = 10, then m to the second power + n to the second power= Explain why

The second power of M + the second power of n = (m-n) ^ 2 + 2Mn = 9 + 20 = 29