已知点a 2 0 b 0 2 c cosa sina 0为坐标原点且0
问题描述:
已知点a 2 0 b 0 2 c cosa sina 0为坐标原点且0
答
AC向量=(cosa-2,sina),BC向量=(cosa,sina-2),AC⊥BC,则有cos^2a-2cosa+sin^2a-sina=0,即sina+cosa=1/2,由辅助角公式,sin(a+π/4)=1/2,则a=7π/12.sina=sin(π/2+π/12)=cos(π/4-π/6)=(√2+√6)/4.cosa=cos(π/2+π...