锐角解三角函数,已知在三角形ABC中,角C是90.1比SINA+1比TANA=5,问COSA
问题描述:
锐角解三角函数,已知在三角形ABC中,角C是90.1比SINA+1比TANA=5,问COSA
答
cos^2+sin^2=1 1/sinA+1/tanA=5 tanA=cosA/sinA (1+cosA)/sinA=5
(1+2cosA+cos^2)/25=sinA^2
1+2cosA+cosA^2=25-25cosA^2
(cosA+1)(13cosA-12)=0
cosA=-1 cosA=12/13