Suppose that the price p (in dollars) and the demand x (in thousand of units) of a commodity satisfy the demand equation 6p+x+xp=94
How fast is demand changing when the price is set at $9 and the price is rising at the rate of $2 per week?
dx/dt
=
The demand is decreasing at the rate of _________units per week.

Respuesta :

The demand is decreasing at the rate of 2units per week.

Given the price p (in dollars) and the demand x (in thousands of units) of a commodity satisfy the demand equation 6p+x+xp=94

Differentiating the function with respect to time will result in;

[tex]6\frac{dp}{dt}+\frac{dx}{dt} + x \frac{dp}{dt} + p\frac{dx}{dt} = 0[/tex]

Given the following paramters

p = $6

dp/dt = $2/wk

Substitute the given parameters into the formula to have:

[tex]6(2)+\frac{dx}{dt} + 2x + 9\frac{dx}{dt} = 0[/tex]

To get the demand x, we will simply substitute  p = 9 into the expression to have:

6(9)+x+9x=94

10x+54 = 94

10x = 94 - 54

10x = 40

x = 4

Substitute x = 4 into the derivative to have:

[tex]6(2)+\frac{dx}{dt} + 2x + 9\frac{dx}{dt} = 0\\6(2)+\frac{dx}{dt} + 2(4) + 9\frac{dx}{dt} = 0\\6(2)+\frac{dx}{dt} + 8 + 9\frac{dx}{dt} = 0\\20 + 10\frac{dx}{dt} =0\\10\frac{dx}{dt} =-20\\\frac{dx}{dt} =\frac{-20}{10}\\\frac{dx}{dt} =-\$2/wk[/tex]

Hence the demand is decreasing at the rate of 2units per week.

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