3.When production is 2100, marginal revenue is 6.75 dollars per unit and margina
ID: 2842910 • Letter: 3
Question
3.When production is 2100, marginal revenue is 6.75 dollars per unit and marginal cost is 7.75 dollars per unit. Do you expect maximum profit to occur at a production level above or below 2100? (Enter above or below.)
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Explanation / Answer
can find the average slope on the interval by looking at change in y / change in x at the end points.
avg slope = f(5)-f(3) / 5 - 3 = 2sqrt(5)+3-2sqrt(3)-3 / 5-3 = 2 ( sqrt(5)-sqrt(3)) / 2 = sqrt(5) - sqrt(3)
Then you are looking for the point c in this interval where the actual slope is equal to this value. In other words you want the point where the tangent line to the curve is parallel to the line between the two points (2, f(2)) and (5 , f(5)).
Take the derivative of f(x) and set it equal to the value we got for avg slope,
f(x) = 2x^1/2 +3 ( I like to rewrite the sqrt first. It helps when differentiating)
f'(x) = 2(1/2)x^-1/2 = x^-1/2
so want sqrt(5) - sqrt(3) = x^-1/2
sqrt(5) - sqrt(3) = 1/sqrt(x)
sqrt(x) = 1/(sqrt(5)-sqrt(3))
x = (1 / (sqrt(5) - sqrt(3)))^2
x = 3.9365...
Obviously since we are dealing with square roots of primes this is an approximate value. If you need the exact just leave it in the second to last form. That's as simplified as you're going to get.
An easy check is to make sure your value is actually in the interval. You can also double check by plugging this back into the derivative formula you solved for and check it against the avg slope. They should be equal.
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