how do you expand double brackets?

Answer 1

give an example, or try google first.

Answer 2

to expand double brackets you use FOIL

for example
(a+4)(a+2)
for this one you get A from the first set of bracket and multiply (a+2) which becomes: a^2+2a
then you get 4 from the first set of brackets and multiply (a+2) which becomes: 4a +8 (4*2=8)
and you put a^2+2a and 4a +8 together and becomes a^2+2a+4a+8 and add 2a+4a which becomes 6a
so the final answer is a^2+6a+8

(a+4)(a+2)
=a^2+2a+4a+8
=a^2+6a+8

Answer 3

(a+4)(a+2)
when in danger or in doubt:
(a+4)(a+2)
is the same as
a (a+2) + 4(a+2)
= a^2 + 2 a + 4 a + 8
= a^2 + 6 a + 8
You do not really need that for a FOIL problem, but keep it in mind for when things get messier.

Answer 4

for distributive property see:
https://www.mathsisfun.com/definitions/distributive-law.html