About a pair of vectors and the value of its sum norm

Question

Knowing that |u|=11, |v|=23 and |u-v|=30 how can i calculate |u+v| (where || denotes the norm of a vector)?

Answer 1

Hint: The Parallelogram Law states that $\|u+v\|^2 + \|u-v\|^2 = 2\|u\|^2+2\|v\|^2$.