w_dahai
幼苗
共回答了18个问题采纳率:77.8% 举报
(1)角ABO也是β,所以有:角AOB+2β=π,角AOB=π-2β,则α=π/2+角AOB=3π/2-2β
(2)B的坐标即为(cosα,sinα),cosα=cos(3π/2-2β)=-cos(π/2-2β)=-sin2β=-2sinβcosβ=-2*4/5*3/5=-24/25;sinα=sin(3π/2-2β)=-sin(π/2-2β)=-cos2β=(sinβ)^2-(cosβ)^2=(4/5)^2-(3/5)^2=7/25
(3)xB-yB=cosα-sinα=cos2β-sin2β=根号2(cosπ/4*cos2β-sinπ/4*sin2β)=根号2*cos(π/4+2β),当β=3π/8时,最小为负根号2
1年前
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