【注:sin2x=2sinxcosx. sin(π-x)=sinx】原式=(1/2)×2sin(5π/12)cos(5π/12)=(1/2)sin(5π/6)=(1/2)sin[π-(π/6)]=(1/2)sin(π/6)=(1/2)×(1/2)=1/4.∴原式=1/4.
sin5/12π×cos5/12π怎么算?
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