已知向量a=(4,3),b=(-1,2) 1.求a与b的夹角的余弦值 2.若向量a- λb与2a+b垂直,求 λ的值
已知向量a=(4,3),b=(-1,2) 1.求a与b的夹角的余弦值 2.若向量a- λb与2a+b垂直,求 λ的值
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数学人气:809 ℃时间:2019-10-11 05:46:10
优质解答
cosθ = (a · b)/(|a| |b|)= [(4)(- 1) + (3)(2)]/[√(4² + 3²) · √(1² + 2²)] = 2/(5√5)θ = 79.695°a - λb = (4i + 3j) - λ(- i + 2j) = (4 + λ)i + (3 - 2λ)j2a + b = 2(4i + 3j) +...
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