高一数学 a=(sinx/2,根号三cosx/2),b=(cosx/2,cosx/2)向量a=(sinx/2,根号三cosx/2),向量b=(cosx/2,cosx/2),设f(x)=向量a点乘向量b1.求函数f(x)在0到2π闭区间上的零点2.设三角形ABC的对边为abc,知道f(A
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![高一数学 a=(sinx/2,根号三cosx/2),b=(cosx/2,cosx/2)向量a=(sinx/2,根号三cosx/2),向量b=(cosx/2,cosx/2),设f(x)=向量a点乘向量b1.求函数f(x)在0到2π闭区间上的零点2.设三角形ABC的对边为abc,知道f(A](/uploads/image/z/1043674-34-4.jpg?t=%E9%AB%98%E4%B8%80%E6%95%B0%E5%AD%A6+a%3D%EF%BC%88sinx%2F2%2C%E6%A0%B9%E5%8F%B7%E4%B8%89cosx%2F2%EF%BC%89%2Cb%3D%EF%BC%88cosx%2F2%2Ccosx%2F2%EF%BC%89%E5%90%91%E9%87%8Fa%3D%EF%BC%88sinx%2F2%2C%E6%A0%B9%E5%8F%B7%E4%B8%89cosx%2F2%EF%BC%89%2C%E5%90%91%E9%87%8Fb%3D%EF%BC%88cosx%2F2%2Ccosx%2F2%EF%BC%89%2C%E8%AE%BEf%28x%29%3D%E5%90%91%E9%87%8Fa%E7%82%B9%E4%B9%98%E5%90%91%E9%87%8Fb1.%E6%B1%82%E5%87%BD%E6%95%B0f%28x%29%E5%9C%A80%E5%88%B02%CF%80%E9%97%AD%E5%8C%BA%E9%97%B4%E4%B8%8A%E7%9A%84%E9%9B%B6%E7%82%B92.%E8%AE%BE%E4%B8%89%E8%A7%92%E5%BD%A2ABC%E7%9A%84%E5%AF%B9%E8%BE%B9%E4%B8%BAabc%2C%E7%9F%A5%E9%81%93f%EF%BC%88A)
高一数学 a=(sinx/2,根号三cosx/2),b=(cosx/2,cosx/2)向量a=(sinx/2,根号三cosx/2),向量b=(cosx/2,cosx/2),设f(x)=向量a点乘向量b1.求函数f(x)在0到2π闭区间上的零点2.设三角形ABC的对边为abc,知道f(A
高一数学 a=(sinx/2,根号三cosx/2),b=(cosx/2,cosx/2)
向量a=(sinx/2,根号三cosx/2),向量b=(cosx/2,cosx/2),设f(x)=向量a点乘向量b
1.求函数f(x)在0到2π闭区间上的零点
2.设三角形ABC的对边为abc,知道f(A)=根号三,b=2,sinA=2sinC,求c的值
告急求解 麻烦写详细点
高一数学 a=(sinx/2,根号三cosx/2),b=(cosx/2,cosx/2)向量a=(sinx/2,根号三cosx/2),向量b=(cosx/2,cosx/2),设f(x)=向量a点乘向量b1.求函数f(x)在0到2π闭区间上的零点2.设三角形ABC的对边为abc,知道f(A
1.f(x)=ab=sinx/2cosx/2+√3cosx/2cosx/2=1/2sinx+√3(1+cosx)/2=1/2sinx+√3/2cosx+√3/2
=sin(x+π/3)+√3/2
f(x)=0,∴x+π/3=2kπ-π/3或者x+π/3=2kπ-2π/3,∴x=2kπ-2π/3或者x=2kπ-π
当x在0到2π上时,x=4π/3或x=π.
2.f(A)=sin(A+π/3)+√3/2=√3,∴A=π/3
∵sinA=2sinC,∴a=2c
∴cosA=1/2=(b²+c²-a²)/2bc=(4+c²-4c²)/4c
解得3c²+2c-4=0,c=(-2+√13)/3