Try It Yourself#

Exercise 1#

Implicit differentiation

Find dydx where y is defined implicitly by y4+x3y2x=5.

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Answer: (13x2y2)/(4y3+2x3y)

Exercise 2#

Equation of tangent line via implicit differentiation

Find the equation of the line tangent to the curve defined implicitly by x4yx3+14y=29 at the point (1,2).

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Answer: y=x/3+7/3

Exercise 3#

Elasticity of demand using implicit differentiation

The demand equation for Hager & Little’s Better Business Calculus book series is given by

p=5x22x+100

where p is the wholesale unit price in dollars and x is the quantity demanded in units of a thousand. Compute the elasticity of demand when x=4.

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Answer: 1/14

Exercise 4#

Related rates problem: demand vs. revenue

A company is increasing production of math-brain protein bars at a rate of 50 cases per day. All cases produced can be sold. The daily demand function is given by

p(x)=80x100

where x is the number of cases produced and sold, and p is in dollars. Find the rate of change of the revenue with respect to the time in days when daily production is 500 cases.

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Answer: revenue increases by $3,500 per day

Exercise 5#

Related rates problem: price vs. demand

If the quantity demanded daily of a product is related to its unit price in dollars by

p2=106x2,

how fast is the quantity demanded changing when x=5 and the unit price is decreasing at a rate of $3 per day?

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Answer: demand increases by 27/5 units per day

Exercise 6#

Related rates problem: price vs. demand

The weekly demand function is given by

p+x+3xp=43

where x is the number of thousands of units demanded weekly and p is in dollars. If the price is increasing at a rate of 20 cents per week when the level of demand is 4000 units, at what rate is the demand decreasing?

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Answer: demand decreases by 260 units per week