✔ 最佳答案
1. cos(40°-3﹫)=sin(7﹫+2°)
sin(90°-40°+3@)=sin(7@+2°)
50+3@=7@+2
4@=48
@=12
2008-05-13 19:41:40 補充:
2. cos37°sin53°+cos53°sin37°
=sin(90-37)sin53+cos53cos(90-37)
=sin53sin53+cos53cos53
=(sin53)^2+(cos53)^2
=1
2008-05-13 19:42:00 補充:
^2=2次
2008-05-13 19:54:47 補充:
(sin19°tan71°-cos19°)^2
=(sin19X(cos19÷sin19)-cos19)^2
=0^2
=0
2008-05-13 20:00:15 補充:
(cos﹫+1)(cos﹫-1)≡﹣sin﹫cos﹫tan﹫
R.H.S.
=﹣sin﹫cos﹫tan﹫
=-sin@cos@(sin@÷cos@)
=-(sin@)^2
=-(1-(cos@)^2))
=(cos@)^2)-1
=(cos﹫+1)(cos﹫-1) <---------------x^2-y^2=(x+y)(x-y)
=L.H.S.