Final answer:
3) Tangent
The tangent angle used in trigonometry for calculating the difference in length of an equal spread offset is the Tangent, which is the ratio of the opposite to adjacent sides of a right triangle.
Step-by-step explanation:
When calculating the difference in length of an equal spread offset using Trigonometry, the tangent angle used is the Tangent. The tangent of an angle in a right triangle is the ratio of the length of the opposite side to the length of the adjacent side. In the context of vector addition, trigonometric relationships such as sine and cosine are also used to find the components of a vector when the magnitude and angle are known.