Tan means tangent. In a right triangle, if the acute angle α is determined, then the ratio of the opposite side to the adjacent side of the angle α is determined. This ratio is called the tangent of angle α, and is written as tanA.

In Rt△ABC (right triangle), ∠C = 90, AB is the opposite side C of ∠ C, BC is the opposite side A of ∠A, AC is the opposite side B of ∠B, and the tangent function is tanB=b/a, that is, tanB=AC/BC. ?

Extended data:

In a plane triangle, the tangent theorem shows that the quotient obtained by dividing the sum of any two sides by the difference between the first side and the second side is equal to the quotient obtained by dividing the tangent of half the sum of the diagonals of these two sides by the tangent of the difference between the diagonals of the first side and the second side.

Tangent theorem: (a+b)/(a-b) = tan ((α+β)/2)/tan ((α-β)/2)