sin50(1+tan60tan10)

显示全部楼层 · 2009-7-18 19:43:50

=sin50[1+(sin60/cos60)*(sin10/cos10)] =sin50[1+(sin60*sin10)/(cos60*cos10)] =sin50[(sin10*sin60+cos10*cos60)/(cos10*cos60)]=sin50[cos(60-10)/(cos10*cos60)]=sin50[cos50/(cos10*cos60)] =(sin50*cos50)/(cos10*cos60) =sin100/(2*cos10*cos60) =sin80/(2*cos10*cos60)=cos10/(2*cos10*cos60) =1/(2cos60) =1...

千问 · 2009-7-18 19:43:50

1...

千问 · 2009-7-18 19:43:50

1...

千问 · 2009-7-18 19:43:50

1...

千问 · 2009-7-18 19:43:50

因为tan50°=tan(60°-10°)=(tan60°-tan10°)/(1+√3tan10°)sin50*(1+tan60*tan10)=cos50°*(tan60°-tan10°)*(1+√3*tan10)/(1+√3tan10°)=cos50°(tan60°-tan10°)=cos50°(sin60°/cos60°-sin1...