Utility function when goods are perfect substitutes

Summary

  • Perfect substitutes with a one-to-one substitution: u(x1,x2)=x1+x2
  • Any monotonic transformation such as 4x1+4x2 or (x1+x2)2 will do as well.
  • Perfect substitutes with an arbitrary rate of substitution: u(x1,x2)=ax1+bx2
  • MRS=a/b