2. Let g, Q E R3 be 3-dimensional vectors. Prove that y and y are perpendicular if and only if \"v w|[ = ||v+w||. (Note: Here you have to prove an 'z'f and only if' statement. This means, you have to prove the following two things: 1: If y is perpendicular to Q then ||v wll = \"U + wll. 2: If ||v w|| = ||v +w|| then y is perpendicular to Q.)