因为:
5sinb = sin(2a+b) = sin(a+b +a) = sin(a+b)cosa + cos(a+b)sina,
而:
sinb = sin(a+b-a) = sin(a+b)cosa - cos(a+b)sina
因此:
5sin(a+b)cosa - 5cos(a+b)sina = sin(a+b)cosa + cos(a+b)sina
化简:
4sin(a+b)cosa = 6cos(a+b)sina,
tan(a+b)/tana = 6/4 = 3/2
因为:
5sinb = sin(2a+b) = sin(a+b +a) = sin(a+b)cosa + cos(a+b)sina,
而:
sinb = sin(a+b-a) = sin(a+b)cosa - cos(a+b)sina
因此:
5sin(a+b)cosa - 5cos(a+b)sina = sin(a+b)cosa + cos(a+b)sina
化简:
4sin(a+b)cosa = 6cos(a+b)sina,
tan(a+b)/tana = 6/4 = 3/2