sin20sin40sin60sin80

sin20sin40sin60sin80 =(1/2)[2sin20cos50](¡Ì3/2)sin80 =(¡Ì3/4)[sin70-sin30]cos10 =(¡Ì3/4)[sin70cos10]-(¡Ì3/4)sin30cos10 =(¡Ì3/8)[sin8...

sin20sin40sin60sin80 20 40±íʾ¶ÈÊý

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sin20*sin40*sin60*sin80=?('*'Ϊ³Ë)ºÇºÇ...

(20¡ã+40¡ã)]sin80¡ãsin60¡ã/2 =(cos20¡ãsin80¡ã-cos60¡ãsin80¡ã)sin60¡ã/2 ={[sin(20¡ã+80¡ã)+sin(80¡ã-20¡ã)]/2-sin80¡ã/2}sin60¡ã/2 ={[sin100¡ã+sin60...

sin20¡ãsin40¡ãsin80¡ã=?

sin20sin40sin80 =-1/2(cos60-cos20)sin80 =-1/4*sin80+1/2*cos20*sin80 =-1/4*sin80+1/2*[1/2*(sin60+sin100)] =-1/4*sin80+1/4*sin60+1/4...

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sin20sin40sin60sin80=?

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sin20+sin40-sin80=sin(30-10)+sin(30+10)-cos10=sin30cos10-cos30sin10+sin30cos10+cos30sin10-cos10=cos10-cos10=0

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ÓÐ\sin 60^\circ=\sin 3\times 20^\circ =4\sin20^\circ\sin40^\circ\sin80^\circ.Ôò\begin{gather*} \sin 20^\circ\sin 80^\...

Çósin10cos20sin30cos40sin50cos60sin70cos80sin90µÄÖµ

sin10=cos80cos20=sin70sin30=cos60cos40=sin50sin90=1sin10cos20sin30cos40sin50cos60sin70cos80sin90=(sin10cos20sin30cos40)^2=(sin10cos10cos20sin30cos40)...

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