单位圆O圆O和直线y=x交于A(1,1)A(-1,-1).A,A': sinx=cosx=√2/2
(sinx)^2=(cosx)^2y=x和y轴间(锐角区域),sinx>cosx圆O和y=-x交于B(-1,1),B'(1,-1)B,B' sinx=-cosx=-√2/2
(sinx)^2=(cosx)^2y=-x和y轴间(锐角区域), BO和y轴间 sinx> -cosx>=0
(sinx)^2>(cosx)^2 B'O和y轴间:-sinx>cosx>=0
(sinx)^2>(cosx)^2因此π/4+2k ...
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