直角三角形中,直角边a,b,斜边c
sinx=a/c cosx=b/c a^2+b^2=c^2
(sinx)^2+(cosx)^2=a^2/c^2+b^2/c^2=(a^2+b^2)/c^2=c^2/c^2=1
(sinx)^2+(cosx)^2=1