中三Math (三角比的關係)

To be more precise,

(3sin r - 4cos r) / (3sin r+4cos r)
=[(3sin r - 4cos r)/cos r] / [(3sin r+4cos r) / cos r]
= (3tan r - 4)/ (3tan r + 4)
= (3(3/4)-4) / (3(3/4)+4)
= (-7/4)/(25/4)
=-7/25

2007-08-25 22:35:19 補充：
tan r = 3/4 並不代表 sin r = 3/5 和 cos r = 4/5sin r和 cos r 可以係負數...但係中四的數學...