Please answer the following:

\f(1 point} Let it, ? 6 R\" with |||| = 5 and \"it\" = 7. Prove that ||+ t\" = 12 itand only \"5131 = W. There are two parts to the proof. Part 1: Suppose 5113 2 7'3. Then 11? : end it + '11} : \"3.5+ if = Thusll+ll=ll 17"\": \"ll: Part2: Suppose || + ti?\" = 12. By the triangularinequal'rty, ||+ 13\" 3 \"if\" + H1?\" = It follows that if and 1?: are in the same direction, Le. . Where I: = . Hence 5115 = 75. Q.E. D