Question

向量|a|=2,向量|b|=3,且向量a×向量b=5,求向量|2a-b|,

Answer 1

a×b=|a|×|b|×sin=2×3×sin=5

所以sin=5/6

|2a-b|^2 =4a^2-2×2a×b + b^2

=4×4-4×(5/6) + 9