Which of these is a linear function?
f(x)=x2f(x) = x^2f(x)=x2
f(x)=3x−4f(x) = 3x - 4f(x)=3x−4
f(x)=1/xf(x) = 1/xf(x)=1/x
f(x)=∣x∣f(x) = |x|f(x)=∣x∣