Sin(180度+A)Cos(180-A)= -sin(A) * -cos(A) = sin(A)cos(A)
另一方面：
(SinA+COSA)/(SinA-CosA)=2 ===〉
(SinA+COSA) = 2(SinA-CosA)
两边平方：
[sin(A)]^2 + [cos(A)]^2 + 2sin(A)cos(A) =
4[sin(A)]^2 + 4[cos(A)]^2 - 8sin(A)cos(A) ===>
1 + 2sin(A)cos(A) = 4 - 8sin(A)cos(A) ====>
10sin(A)cos(A) = 3 ====>
sin(A)cos(A) = 3/10 ====>
Sin(180度+A)Cos(180-A) = 0.3