# Business MathFind Price Elasticity of Demand

#### mathkid3

##### New member
Find price elasticity of demand for the demand function at the indicated x-value.

Is the demand elastic, inelastic or of unit elasticity at the indicated x-value?

Use a graphing utility to graph the revenue function, and identify the intervals of elasticity and inelasticity.

... I will list all information I can to help someone to help me to solve and understand the problem.

Demand Function = p = (500)/(x^2) + 5

x-value = 5

The following may be of help as well...

Definition of Price Elasticity of Demand - If p = f(x) is a differentiable function, then the price elasticity of demand is given by

N = (p/x)/(dp/dx)

where N is the lowercase Greek letter eta. For a given price, the demand is elastic when abs(absolute) value N > 1, the demand is inelastic when abs N < 1, and the demand has unit elasticity when abs N = 1

Thanks in advance for any and all assistance on this Calculus problem

-mathkid3

#### MarkFL

Staff member
Well, I would begin by computing $\displaystyle \frac{dp}{dx}|_{x=5}$

Next, I would compute $\displaystyle \frac{p(5)}{5}$.

Once you have these two numbers, then compute their quotient to get the price elasticity of demand $\displaystyle \eta$.

Now, let's see what you get...

By the way, this site also supports the rendering of $\displaystyle \LaTeX$. The difference is (at least the way I do it) is to enclose your code with the tags:

Code:
$\displaystyle insert code here$

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#### mathkid3

##### New member
Mark,

so glad you are on this site and you have already helped me so much with understanding some of these Calculus problems.

ok ..let's see.....

You said first to find the derV of p so I get

(x-1000)/(x^3)

next you say find p(5)/(5)

Areyou saying to plug 5 into the original function and then divided the outcome by 5?

if so I get x = 5

am I correct thus far and if so tell me again what to do next?

If I am not correct, would you explain to me again what to do ?

Thank You

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#### CaptainBlack

##### Well-known member
The following may be of help as well...

Definition of Price Elasticity of Demand - If p = f(x) is a differentiable function, then the price elasticity of demand is given by

N = (p/x)/(dp/dx)

where N is the lowercase Greek letter eta. For a given price, the demand is elastic when abs(absolute) value N > 1, the demand is inelastic when abs N < 1, and the demand has unit elasticity when abs N = 1
$E_d=\frac{p}{x \frac{dp}{dx}}$
$E_d=\frac{x}{p}\frac{dp}{dx}$
(Note that the Wikipedia page uses $$Q$$ for demand (quantity) and $$P$$ for price).
Now the table the Wikipedia page gives for interpreting $$E_p$$ is exactly the same as that given above by you, so there is a mistake somewhere.