已知函数f(X)=2sin(x-π/3)cos(x-π/3)+2根号3cos^2(x-π/3)-根号3,若函数y=f(2

问题描述:

已知函数f(X)=2sin(x-π/3)cos(x-π/3)+2根号3cos^2(x-π/3)-根号3,若函数y=f(2x)-a在区间
[0,π/4]上恰有两个零点x1,x2,求tan(x1+x2)的值
1个回答 分类:数学 2014-10-28

问题解答:

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f(x)=2sin(x-π/3)cos(x-π/3)+2√3cos^2(x-π/3)-√3
  =sin(2x-2π/3)+√3cos(2x-2π/3)
  =2[sin(2x-2π/3)cosπ/3+cos(2x-2π/3sinπ/3]
  =2sin(2x-2π/3+π/3)+1-√3
  =2sin(2x-π/3)
  故 f(2x)-a=2sin(4x-π/3)-a
  当4x-π/3=π/2+kπ 时,y取最大值,此时x=5π/24+kπ(k∈Z).
  又∵在区间[0,π/4]中
  ∴对称轴为x=5π/24
  ∵两零点x1和x2关于x=5π/24对称.
  ∴x1+x2=5π/12
  故tan(x1+x2)=tan(5π/12)
  =tan(π/4+π/6)
  =(1+√3 /3)/(1-√3 /3)
  =2+√3
 
 
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