✔ 最佳答案
if you want to improve your maths... don't jump steps to save your time when processing... try to present it step by step and you will finally be improved as well as your presentation.
by the way, most (not all) of formula can be derived by yourself with very simple principle,
such as (a^b) x (a^c) = a^(b+c)
a^b = a x a x ... x a => total number of a is b
a^c = a x a x ... x a => total number of a is c
thus, (a^b) x (a^c) => total number of a is (b+c) = a^(b+c)
....etc