pre calculus help thanks its appreciated im desperate for help?

Question

find f o g and g o f and find the domain of each function and each composite function in interval notation

f(x)= absolute value of x, g(x) = 2x^3

f(x) = 1/x, g(x) = x + 3

f(x) = 3/x^2-1 ,g(x) = x + 1

Answer 1

isn't this a simple substitution of x?

f[g(x)] = f(2 x^3) = |2x^3| domain all real value
g[f(x)] = g(|x|) = 2 |x| ^ 3 all real value

f[g(x)] = f(x+3) = 1/(x+3) all real except x = -3
g[f(x)] = g(1/x) = 1/x + 3 all real except x = 0

f[g(x)] = f(x+1) = 3/(x+1)^2 -1 all real except x = -1
g[f(x)] = g(3/x^2 -1) = 3/x^2 all real except x = 0