设函数f(x)=sinx-cosx+x+1,0<x<2π,求函数f(x)的单调区间与极值

1个回答

  • 解析:

    f(x)=sinx-cosx+x+1

    则f'(x)=cosx+sinx+1

    =√2(√2/2cosx+√2/2sinx)+1

    =√2(sinπ/4cosx+cosπ/4sinx)+1

    =√2sin(x+π/4)+1.

    令0<x+π/4<π/2且3π/2<x<2π

    得-π/4<x<π/4且5π/4<x<7π/4

    所以函数f(x)的单调增区间为(-π/4,π/4)∪(5π/4,7π/4)

    令π/2<x+π/4<3π/2

    得π/4<x<5π/4

    所以函数f(x)的单调减区间为(π/4,5π/4)

    所以函数f(x)的极大值为f(π/4)=√2+1

    极小值为f(5π/4)=1-√2.