y=cos2x+sinx(-π/6

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y=cos2x+sinx(-π/6
y=cos2x+sinx(-π/6

y=cos2x+sinx(-π/6
y=cos2x+sinx=1-2(sinx)^2+sinx
-π/6

y=cos2x+sinx(-π/6 <=x<= 2π/3),=1-2sinx^2+sinx=-2(sinx-1/4)^2+9/8
(-π/6 <=x<= 2π/3), -1/2<=sinx<=1
sinx=1/4 最大值9/8
sinx=1或者-1/2 最小值0
最小值加最大值之和9/8