Question

问数学问题 详细如图

问数学问题 详细如图向量的题目

Answer 1

令C = a·b = b·c = c·a
a = -2b - 3c
C = a·b = (-2b-3c)·b  = -2|b|²- 3b·c = -2|b|²- 3C
|b|² = -2C
C = c·a = c·(-2b-3c) = -2b·c - 3|c|² = -2C - 3|c|²
|c|² = -C
C < 0
b·c =C = |b||c|cosθ = √(-2C)√(-C)cosθ = -√2Ccosθ
cosθ = -√2/2
θ = 3π/4