finding an expression for functions?

Question

if f(x) = (x^2 +1) if x ≤ 0
(-x) if x > 0

and g(x) = (1+x) if x ≤ 0
(2x) if x > 0

what are the expressions for:

1. f + g
2. f ○ g
3. g ○ f

Answer 1

The answers are derived by addition and substitution:
1.
f + g = x^2 + x + 1, x ≤ 0
f + g = x, x> 0

2.
f(g) = ((1+x)^2 +1) if x ≤ 0
(-2x) if x > 0

3.
g(f) = (1+ x^2 +1) if x ≤ 0
(-2x) if x > 0