Consider two functions y1 (x) = x and y2 (x) = |x|. Then:
1
both functions are linearly dependent on the real line.
2
y1(x) is linearly independent but y2(x) is linearly dependent on the real line.
3
y1(x) is linearly dependent but y2(x) is linearly dependent on the real line.
4
both functions are linearly independent on the real line.