若非零向量a b满足|a|=|b|,(2a+b)b=0则a与b的夹角为A,30° B,60° C,120° D,150°

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若非零向量a b满足|a|=|b|,(2a+b)b=0则a与b的夹角为A,30° B,60° C,120° D,150°
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若非零向量a b满足|a|=|b|,(2a+b)b=0则a与b的夹角为A,30° B,60° C,120° D,150°
若非零向量a b满足|a|=|b|,(2a+b)b=0则a与b的夹角为
A,30° B,60° C,120° D,150°

若非零向量a b满足|a|=|b|,(2a+b)b=0则a与b的夹角为A,30° B,60° C,120° D,150°
选C
(2a+b)·b=0
2a·b+b·b=0
2a·b=-|b|²
a·b=-|b|²/2
于是
cos=a·b/|a||b|
=(-|b|²)/2|a||b|
=-1/2
所以夹角为120º