Symbols I and J are most commonly used to represent imaginary unit I? =j？ = 1, general math books use I, and some books use J.

Also, in the three-dimensional rectangular coordinate system, the horizontal axis, vertical axis and vertical axis are usually expressed as I, J and K.

In analytic geometry, p represents the focal length and ρ represents the length of the polar diameter.

K and t are very common in parametric equations and are usually used as setting position parameters.

Symbols represent different meanings on different occasions, and understanding their meanings requires you to fully understand the relevant knowledge of the article. The above is just the general default usage, and no special explanation is needed.