若sinа=(m-3)/(m+5),cosа=(4-2m)/(m+5),其中π/2

问题描述:

若sinа=(m-3)/(m+5),cosа=(4-2m)/(m+5),其中π/2

因为sin^2а+cos^2a=1,π/20,cosа=(4-2m)/(m+5)m3
[(m-3)/(m+5)]^2+[(4-2m)/(m+5)]^2=1
解得:m=8

π/20,m3
(4-2m)/(m+5)=cos(a)2或m3 或m