cos方5π/12+cos方π/12+cosπ/12*cos5π/12 最后等于5/4的过程。求高手~

显示全部楼层 · 2011-11-20 21:13:53

cos25π/12+cos2π/12+cosπ/12*cos5π/12 由于cos5π/12=sin（π/2-5π/12）=sinπ/12原式=sin2π/12+cos2π/12+cosπ/12sinπ/12
=1+?sinπ/6
=1+1/4
=5/4...

千问 · 2011-11-20 21:13:53

cos25π/12+cos2π/12+cosπ/12*cos5π/12 =cos25π/12+sin2(π/2-π/12)+sin(π/2-π/12)*cos5π/12 =cos25π/12+sin25π/12+sin5π/12cos5π/12=1+ (1/2)sin5π/6=1+1...

千问 · 2011-11-20 21:13:53

=(1+cos5π/6)/2+(1+cosπ/6)/2+cosπ/12cos(π/2-π/12)=1+cos5π/6+cosπ/6+cosπ/12sinπ/12=1-√3/2+√3/2+1/2sinπ/6=1+1/4=5/4...