已知向量m=(-1,sinx),n=(-2,cosx),函数f(x)=2mn若△ABC的角A,B所对的边分别为a,b,f(A/2)=24/5,f(B/2+丌/4)=64/13,a+b=11,求a的值
来源:学生作业帮助网 编辑:作业帮 时间:2024/08/15 11:11:01
![已知向量m=(-1,sinx),n=(-2,cosx),函数f(x)=2mn若△ABC的角A,B所对的边分别为a,b,f(A/2)=24/5,f(B/2+丌/4)=64/13,a+b=11,求a的值](/uploads/image/z/1699388-44-8.jpg?t=%E5%B7%B2%E7%9F%A5%E5%90%91%E9%87%8Fm%3D%28-1%2Csinx%29%2Cn%3D%28-2%2Ccosx%29%2C%E5%87%BD%E6%95%B0f%28x%29%3D2mn%E8%8B%A5%E2%96%B3ABC%E7%9A%84%E8%A7%92A%2CB%E6%89%80%E5%AF%B9%E7%9A%84%E8%BE%B9%E5%88%86%E5%88%AB%E4%B8%BAa%2Cb%2Cf%28A%EF%BC%8F2%29%3D24%EF%BC%8F5%2Cf%28B%EF%BC%8F2%2B%E4%B8%8C%EF%BC%8F4%29%3D64%EF%BC%8F13%2Ca%2Bb%3D11%2C%E6%B1%82a%E7%9A%84%E5%80%BC)
xPJ@~,%H$BCc0H[QhЋğ>dzIxO3|?;^bFoa
F8I='{NVfīS6$ auUs
s5M/$H
ދ!G"5vaSNj'QFu/ڥfh&:NߴGOfJ!0Ny!ϪKU\I=Ijd#jZ45ɕT kDhW_%ny4MdK A8
已知向量m=(-1,sinx),n=(-2,cosx),函数f(x)=2mn若△ABC的角A,B所对的边分别为a,b,f(A/2)=24/5,f(B/2+丌/4)=64/13,a+b=11,求a的值
已知向量m=(-1,sinx),n=(-2,cosx),函数f(x)=2mn
若△ABC的角A,B所对的边分别为a,b,f(A/2)=24/5,f(B/2+丌/4)=64/13,a+b=11,求a的值
已知向量m=(-1,sinx),n=(-2,cosx),函数f(x)=2mn若△ABC的角A,B所对的边分别为a,b,f(A/2)=24/5,f(B/2+丌/4)=64/13,a+b=11,求a的值
f(x)=2mn=4+2sinxcosx=sin2x+4,f(A/2)=24/5,得sinA=4/5,
f(B/2+丌/4)=64/13,得cosB=12/13,得sinB=5/13
由正弦定理a/sinA=b/sinB=c/sinC,得5a/4=13b/5,且a+b=11
,得a=52/7