20+ Tan Formula X/Y. For the functions sin, cos, sec, and csc with period 2π, half a turn is half their period. Expression of hyperbolic functions in terms of others.
Tan(x y) = (tan x tan y) / (1 tan x tan y).
If x < 0 use the appropriate sign as indicated by formulas in the section functions of negative arguments. Tan(x y) = (tan x tan y) / (1 tan x tan y). We can also use the tangent formula to find the angle between two lines. In case you need it, here is the triangle angle calculator, and the right triangle angle and side calculator.