diketahui cos(x-y)=4/5 dan sinx.siny=3/10 nilai tanx.tany

cos(x - y) = 4/5
cos x cos y + sin x sin y  = 4/5
cos x co y + 3/10  = 4/5
cos x cos y = 4/5 - 3/10 = 1/2

tan x .tan y = (sin x . sin y)/(cos x . cos y) = (3/10)/ (1/2) = 3/5