sin2π/5 +cos26π/5 + 2cos3π * sin5π/6 的值为

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sin2π/5+cos26π/5+2cos3π*sin5π/6的值为sin2π/5+cos26π/5+2cos3π*sin5π/6的值为sin2π/5+cos26π/5+2cos3π*sin5π/6的

sin2π/5 +cos26π/5 + 2cos3π * sin5π/6 的值为
sin2π/5 +cos26π/5 + 2cos3π * sin5π/6 的值为

sin2π/5 +cos26π/5 + 2cos3π * sin5π/6 的值为

sin2π/5 +cos26π/5 + 2cos3π * sin5π/6
=sin2π/5 +cos(5π+π/5) + 2cosπ * sin(π-π/6)
=sin2π/5 -cosπ/5- sinπ/6
=sin72º -cos36º-1/2
=0.9510 -0.8-1/2
≈-0.349