<p>Point elasticity at price <span class="math-container">$P$</span> is defined as <span class="math-container">$\frac{P}{Q}\times \frac{dQ}{dP}$</span> (therefore it is usually a negative number, but the sign is often omitted). A straight line has a constant ratio <span class="math-container">$\frac{dQ}{dP}$</span> while <span class="math-container">$\frac{P}{Q}$</span> ranges from <span class="math-container">$0$</span> to <span class="math-container">$\infty$</span> (as you can see by moving <span class="math-container">$A$</span> on your plot). Hence, if a demand curve is a straight line with a negative slope the absolute value of its elasticity will range from <span class="math-container">$0$</span> to <span class="math-container">$\infty$</span>. Moreover, any price elasticity of demand curve that can be represented as a straight line will have a region of elastic demand until the point where <span class="math-container">$\frac{Q}{P} = \frac{dQ}{dP}$</span>, after which it will have inelastic demand.</p>
<p>With regards to the image you provided, maybe the notion of &quot;elastic demand&quot; is not used here to describe the whole curve, but to describe a particular region, namely a change from <span class="math-container">$P_1$</span> to <span class="math-container">$P_2$</span>. Anyway, I agree that the image is confusing because it gives an impression that price elasticity depends on absolute value changes, which is not true, and it is hard to compare relative change of <span class="math-container">$P$</span> and <span class="math-container">$Q$</span> because they start from different absolute values and have different absolute changes.</p>

CC BY-SA 4.0
2021-12-18T06:44:07.880Z
Thanks a lot sir for giving a clear explaination. I am really thankful to you :)
Rakesh Poddar
CC BY-SA 4.0
2021-12-18T06:49:06.573Z
No problems! [Here](https://www.52coding.com.cn/2019/02/22/Elasticity%20and%20Its%20Application/#the-variety-of-demand-curves) you can find demand curves for various values of elasticity to better build your intuition.
LudwigNagasena
CC BY-SA 4.0
2021-12-18T06:51:41.510Z
Thank You. I will read it to improve my knowledge.
Rakesh Poddar
CC BY-SA 4.0
2021-12-18T04:01:56.327Z
2021-12-18T06:47:09.787Z
2021-12-18T06:47:09.787Z
LudwigNagasena
<p>Let's say I have an Elastic Demand Curve as shown below
<a href="https://i.sstatic.net/k4qsO.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/k4qsO.png" alt="Elastic Demand Curve" /></a></p>
<p>Now, as this is Elastic Demand Curve (<code>When % Change in Quantity Demanded &gt; % Change in Price, the curve is said to Elastic Demand Curve </code>), <strong>Elasticty should always be &gt; 1</strong>.</p>
<p>But, If I calculate using Geometric Method, <strong>Elasticity at point A is</strong> <code>AM / AP</code>.
<strong>This will give Elasticty at A &lt; 1</strong></p>
<p><strong>I just wanted to know as to why do we get Elasticty &lt; 1 when it's Elastic Demand Curve.</strong></p>
<p>Please enlighten me, as maybe I don't know the different between Elasticity at Point and the Elastic Cuver's Elasticty.</p>

CC BY-SA 4.0
2021-12-14T08:16:12.607Z
Could you please edit your question so that it includes your definition of "*Elastic Demand Curve*"?
Giskard
CC BY-SA 4.0
2021-12-14T08:46:39.170Z
Sure.. I will edit right now
Rakesh Poddar
CC BY-SA 4.0
2021-12-14T08:49:46.913Z
I just included the definition sir
Rakesh Poddar
CC BY-SA 4.0
2021-12-14T11:30:32.883Z
And why do you think that "*this is Elastic Demand Curve*"? Is there anything to support this?
Giskard
CC BY-SA 4.0
2021-12-14T12:26:50.687Z
I think because my Books say that Flatter Demand Curves are Highly Elastic. Just like this image : https://qph.fs.quoracdn.net/main-qimg-c525ccfb4e05e08f5344c22ac4c1ba4e-lq
Rakesh Poddar
<microeconomics><elasticity><demand>
How is Elasticity at point different from Elastic Demand Curve?
Rakesh Poddar
# How is Elasticity at point different from Elastic Demand Curve?

(Asked by: username_0 on 2021-12-14)

Let's say I have an Elastic Demand Curve as shown below
[![Elastic Demand Curve](https://i.sstatic.net/k4qsO.png)](https://i.sstatic.net/k4qsO.png)

Now, as this is Elastic Demand Curve (`When % Change in Quantity Demanded > % Change in Price, the curve is said to Elastic Demand Curve` ), **Elasticty should always be > 1**.

But, If I calculate using Geometric Method, **Elasticity at point A is** `AM / AP`.
**This will give Elasticty at A < 1**

**I just wanted to know as to why do we get Elasticty < 1 when it's Elastic Demand Curve.**

Please enlighten me, as maybe I don't know the different between Elasticity at Point and the Elastic Cuver's Elasticty.

**Tags:** microeconomics, elasticity, demand
> **Comments:**
> **username_1**: Could you please edit your question so that it includes your definition of "*Elastic Demand Curve*"?  
> **username_0**: Sure.. I will edit right now  
> **username_0**: I just included the definition sir  
> **username_1**: And why do you think that "*this is Elastic Demand Curve*"? Is there anything to support this?  
> **username_0**: I think because my Books say that Flatter Demand Curves are Highly Elastic. Just like this image : https://qph.fs.quoracdn.net/main-qimg-c525ccfb4e05e08f5344c22ac4c1ba4e-lq  

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## 1 answers

### Answer by username_2 on 2021-12-18. Score: 2 | Accepted answer

Point elasticity at price $P$ is defined as $\frac{P}{Q}\times \frac{dQ}{dP}$ (therefore it is usually a negative number, but the sign is often omitted). A straight line has a constant ratio $\frac{dQ}{dP}$ while $\frac{P}{Q}$ ranges from $0$ to $\infty$ (as you can see by moving $A$ on your plot). Hence, if a demand curve is a straight line with a negative slope the absolute value of its elasticity will range from $0$ to $\infty$. Moreover, any price elasticity of demand curve that can be represented as a straight line will have a region of elastic demand until the point where $\frac{Q}{P} = \frac{dQ}{dP}$, after which it will have inelastic demand.

With regards to the image you provided, maybe the notion of "elastic demand" is not used here to describe the whole curve, but to describe a particular region, namely a change from $P\_1$ to $P\_2$. Anyway, I agree that the image is confusing because it gives an impression that price elasticity depends on absolute value changes, which is not true, and it is hard to compare relative change of $P$ and $Q$ because they start from different absolute values and have different absolute changes.

> **Comments:**
> **username_0**: Thanks a lot sir for giving a clear explaination. I am really thankful to you :)  
> **username_2**: No problems! [Here](https://www.52coding.com.cn/2019/02/22/Elasticity%20and%20Its%20Application/#the-variety-of-demand-curves) you can find demand curves for various values of elasticity to better build your intuition.  
> **username_0**: Thank You. I will read it to improve my knowledge.  

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