Question

A company has found that the number of items sold, x, depends upon
the price, p at which they're sold, according the equation
X=14400-3p^2

The price has been increasing by $2 per month. Find the rate at which
revenue is changing when the price is $40. Note: the answer might be
negative

Answer 1

Answer: -$480

Step-by-step explanation:

The revenue us P*x

now, when P = $40, we have:

X = 14400 - 3*40^2 = 9600

then the revenue is:

9600*$40 = $384000

now, the price increaces by $2 so the new equation is:

X = 14400 - 3*42^2 = 9108

The revenue is:

9109*$42 = $382536

You can see that the revenua is smaller than before.

Now, if we want to calculate the rate of change when p = $40, we need to look at X'(40)

this is:

X´(p) = -3*2*p

then:

X'(40) = -3*2*40 = -120

Theh rate of change of the revenua will be:

X'(40)*$40 = -120*$40 = -$480