In a right triangle, cotangent function of angle A: cotA= adjacent side/opposite side.

cotA= 1/tanA。

cotA*tanA= 1。

1+ Kurt 2A = CSC 2A(CSCA = 1/ Sina) These are all in the book. You can look at the basics and remember them well. I couldn't recite the previous formulas. Later, my deskmate recommended me how to memorize knowledge points efficiently and how to use these knowledge points to do problems. You can go to them.