u = - 4 i + 1 j
v = 4 i + 1 j
| u | = √ (-4)² + 1² = √ 17
| v | = √4² + 1² = √ 17
| u + v | = √(u + v)²=
= √( u² + 2 u v + v² )= ...
cos ( u, v ) = (-16+1) / (|u| |v|) = -15/17
...= √(17 + 2 · √17 · √17 · ( -15/17) +17) =
= √ 34 - 30 = √ 4 = 2
Answer: C ) 2