已知向量a=(4,5cosα),b=(3,-4tanα)(1)若a平行于b,试求sinα;(2)若a⊥b,且α属于(0,π/2),求cos()已知向量a=(4,5cosα),b=(3,-4tanα)(1)若a平行于b,试求sinα;(2)若a⊥b,且α属于(0,π/2),求cos(2α-π/4)的值
来源:学生作业帮助网 编辑:作业帮 时间:2024/07/04 00:54:29
![已知向量a=(4,5cosα),b=(3,-4tanα)(1)若a平行于b,试求sinα;(2)若a⊥b,且α属于(0,π/2),求cos()已知向量a=(4,5cosα),b=(3,-4tanα)(1)若a平行于b,试求sinα;(2)若a⊥b,且α属于(0,π/2),求cos(2α-π/4)的值](/uploads/image/z/10761751-55-1.jpg?t=%E5%B7%B2%E7%9F%A5%E5%90%91%E9%87%8Fa%3D%284%2C5cos%CE%B1%29%2Cb%3D%283%2C-4tan%CE%B1%29%281%29%E8%8B%A5a%E5%B9%B3%E8%A1%8C%E4%BA%8Eb%2C%E8%AF%95%E6%B1%82sin%CE%B1%3B%282%29%E8%8B%A5a%E2%8A%A5b%2C%E4%B8%94%CE%B1%E5%B1%9E%E4%BA%8E%280%2C%CF%80%2F2%29%2C%E6%B1%82cos%EF%BC%88%EF%BC%89%E5%B7%B2%E7%9F%A5%E5%90%91%E9%87%8Fa%3D%284%2C5cos%CE%B1%29%2Cb%3D%283%2C-4tan%CE%B1%29%281%29%E8%8B%A5a%E5%B9%B3%E8%A1%8C%E4%BA%8Eb%2C%E8%AF%95%E6%B1%82sin%CE%B1%3B%282%29%E8%8B%A5a%E2%8A%A5b%2C%E4%B8%94%CE%B1%E5%B1%9E%E4%BA%8E%280%2C%CF%80%2F2%29%2C%E6%B1%82cos%EF%BC%882%CE%B1-%CF%80%2F4%EF%BC%89%E7%9A%84%E5%80%BC)
已知向量a=(4,5cosα),b=(3,-4tanα)(1)若a平行于b,试求sinα;(2)若a⊥b,且α属于(0,π/2),求cos()已知向量a=(4,5cosα),b=(3,-4tanα)(1)若a平行于b,试求sinα;(2)若a⊥b,且α属于(0,π/2),求cos(2α-π/4)的值
已知向量a=(4,5cosα),b=(3,-4tanα)(1)若a平行于b,试求sinα;(2)若a⊥b,且α属于(0,π/2),求cos()
已知向量a=(4,5cosα),b=(3,-4tanα)(1)若a平行于b,试求sinα;(2)若a⊥b,且α属于(0,π/2),求cos(2α-π/4)的值
已知向量a=(4,5cosα),b=(3,-4tanα)(1)若a平行于b,试求sinα;(2)若a⊥b,且α属于(0,π/2),求cos()已知向量a=(4,5cosα),b=(3,-4tanα)(1)若a平行于b,试求sinα;(2)若a⊥b,且α属于(0,π/2),求cos(2α-π/4)的值
向量平行,所以4/3 = 5cosa/(-4tana)
所以4/3 = - 5/4 cos^2a/sina
所以5/4sin^2a - 4/3sina -5/4=0
15sin^2a - 16sina -15=0
(5sina +3)(3sina -5)=0
所以sina = -3/5
如果垂直,则3 * 4 - 20cosa tana = 0 ,所以sina = 3/5
cosa = 4/5
cos(2a-π/4)= cos2a cos(π/4)+sin2a sin(π/4)= (1-2sin^2a) cos(π/4) +2sinacosa
所以都带入就出来了
哥们 你不会是B中的吧----