以知向量a=(sinθ,cosθ-2sinθ),b=(1,2)(1)求a平行b,求tanθ的值(2)若绝对值a=绝对值b,0
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![以知向量a=(sinθ,cosθ-2sinθ),b=(1,2)(1)求a平行b,求tanθ的值(2)若绝对值a=绝对值b,0](/uploads/image/z/5298233-41-3.jpg?t=%E4%BB%A5%E7%9F%A5%E5%90%91%E9%87%8Fa%3D%28sin%CE%B8%2Ccos%CE%B8-2sin%CE%B8%29%2Cb%3D%281%2C2%29%281%29%E6%B1%82a%E5%B9%B3%E8%A1%8Cb%2C%E6%B1%82tan%CE%B8%E7%9A%84%E5%80%BC%282%29%E8%8B%A5%E7%BB%9D%E5%AF%B9%E5%80%BCa%3D%E7%BB%9D%E5%AF%B9%E5%80%BCb%2C0)
以知向量a=(sinθ,cosθ-2sinθ),b=(1,2)(1)求a平行b,求tanθ的值(2)若绝对值a=绝对值b,0
以知向量a=(sinθ,cosθ-2sinθ),b=(1,2)(1)求a平行b,求tanθ的值(2)若绝对值a=绝对值b,0
以知向量a=(sinθ,cosθ-2sinθ),b=(1,2)(1)求a平行b,求tanθ的值(2)若绝对值a=绝对值b,0
a平行b
sinΘ/1=(cosΘ-2sinΘ)/2
sinΘ=cosΘ/2-sinΘ
2sinΘ=cosΘ/2
sinΘ/cosΘ=1/4
tanθ=1/4
|a|=|b|
sin²θ+(cosθ-2sinθ)²=1²+2²
1+4sin²θ-4sinΘcosθ=5
sin²θ-sinΘcosθ=1
(1-cos2Θ)/2-sin2Θ/2=1
cos2Θ+sin2Θ/=-1
根号2sin(2θ+π/4)=-1
sin(2θ+π/4)=-1/(根号2)=-根号2/2
2θ+π/4=(2k+1)π±π/4
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