# How to compare the price elasticity of demand from different points by looking at the graph?

Let's say I have a demand curve looks something like this:

How could I analyze who have the highest or lowest price elasticity of demand?

it seems that the point 1 has highest price or demand? But why? How does the graph tells us that information?

Any helps will be appreicate!

There is no general way of determining elasticity from graph, however linear demand function has a property where demand is infinitely elastic at the top and then elasticity monotonously decreases (in range where $$p>0$$ and $$q>0$$) and is infinitely inelastic at the bottom.
Hence, in the case above you can say that $$\epsilon_1> \epsilon_2 > \epsilon_3$$ (where epsilon denotes elasticity at point $$i$$).
• Thanks for the answer. I am a little bit confused how could we understand why infinitely elastic at the top and then elasticity monotonously decreases? I feel like the elaticity should be all the same on this linear graph since we only looks at percentages changes in quantity v.s percentage changes in price. What am I missing??? Thanks! Apr 27, 2022 at 12:39
• @James elasticity for a general linear demand $D=a-bp$ is given by $\frac{-bp}{a-bp}$ you can plug different numbers into that equation for $p$ and keep parameters of demand $b$ -slope of demand curve and $a$ - y intercept of demand curve constant and you will see that elasticity of linear demand curve is different everywhere.