Hi, i am a bit confused about the positive/negative value of numbers when they are substituted.

Q1. X^2+y^2=25 the points can be negative and positive but the question is when do you put brackets around those negative numbers because sometimes we sub them in without brackets?

Q2. F(x)=x^2 now i know f(2x) = 4x^2 but how about f(-2x) would it be the same?

I would be glad if someone can clear those things for me!

Have a nice day!