A mathematical model written to construct a maximum area rectangle out of a thread of length $10 \mathrm{~cm}$ is given by maximise $l b$. Such that $2(l+b)=10, l, b>0$, where $l$ and $b$ are the length and breadth of the rectangle. This is not a linear programming problem because

• A

  $l$ and $b$ is always positive.
• B

  first constraints is an equation.
• C

  the objective function is no maximise.
• Correct answer
  D

  objective function is not linear.

Hence, the correct answer is option: 'D'.