Cos (x + y) = 3 / 5, cos (x minus y) = 4 / 5

Cos (x + y) = 3 / 5, cos (x minus y) = 4 / 5

cos(x+y)=cosxcosy-sinxsiny=3/5 (1)
cos(x-y)=cosxcosy+sinxsiny=4/5 (2)
(1)+(2) 2cosxcosy=7/5 (3)
(2)-(1) 2sinxsiny= 1/5 (4)
（4）/ (3)
tanx*tany=1/7

Known cos (X-Y) = 1 / 2 cos (x + y) = 1 / 5, find TaNx * tany, please

Cosxcosy + sinxsiny = 1 / 5, ① 1 / 2 (cosxcosy sinxsiny) = 1 / 5, ② from ① and ②, cosxcosy = 3 / 10, sinxsiny = - 1 / 10, tanxtany = (SiNx / cosx) (siny / cosy) = (sinxsiny) / (consxcosy) = - 1 / 3 or more?

If TaNx = 4 / 3, X is in (π, 3 / 2 π), if tany = 1 / 2, prove cos (X-Y) = 2Sin (X-Y)

Best answer on the first floor
tan(x-y)=(tanx-tany)/(1+tanxtany)=1/2
cos(x-y)=2sin(x-y)