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There are local maxima at x = ± 1 , the function is concave up for all x , and the function remains positive for all x .

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For the following exercises, determine

  1. intervals where f is increasing or decreasing and
  2. local minima and maxima of f .

f ( x ) = sin x + sin 3 x over π < x < π

a. Increasing over π 2 < x < π 2 , decreasing over x < π 2 , x > π 2 b. Local maximum at x = π 2 ; local minimum at x = π 2

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For the following exercises, determine a. intervals where f is concave up or concave down, and b. the inflection points of f .

f ( x ) = x 3 4 x 2 + x + 2

a. Concave up for x > 4 3 , concave down for x < 4 3 b. Inflection point at x = 4 3

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For the following exercises, determine

  1. intervals where f is increasing or decreasing,
  2. local minima and maxima of f ,
  3. intervals where f is concave up and concave down, and
  4. the inflection points of f .

f ( x ) = x 3 6 x 2

a. Increasing over x < 0 and x > 4 , decreasing over 0 < x < 4 b. Maximum at x = 0 , minimum at x = 4 c. Concave up for x > 2 , concave down for x < 2 d. Infection point at x = 2

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f ( x ) = x 11 6 x 10

a. Increasing over x < 0 and x > 60 11 , decreasing over 0 < x < 60 11 b. Minimum at x = 60 11 c. Concave down for x < 54 11 , concave up for x > 54 11 d. Inflection point at x = 54 11

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f ( x ) = x + x 2 x 3

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f ( x ) = x 2 + x + 1

a. Increasing over x > 1 2 , decreasing over x < 1 2 b. Minimum at x = 1 2 c. Concave up for all x d. No inflection points

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For the following exercises, determine

  1. intervals where f is increasing or decreasing,
  2. local minima and maxima of f ,
  3. intervals where f is concave up and concave down, and
  4. the inflection points of f . Sketch the curve, then use a calculator to compare your answer. If you cannot determine the exact answer analytically, use a calculator.

[T] f ( x ) = sin ( π x ) cos ( π x ) over x = [ −1 , 1 ]

a. Increases over 1 4 < x < 3 4 , decreases over x > 3 4 and x < 1 4 b. Minimum at x = 1 4 , maximum at x = 3 4 c. Concave up for 3 4 < x < 1 4 , concave down for x < 3 4 and x > 1 4 d. Inflection points at x = 3 4 , x = 1 4

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[T] f ( x ) = x + sin ( 2 x ) over x = [ π 2 , π 2 ]

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[T] f ( x ) = sin x + tan x over ( π 2 , π 2 )

a. Increasing for all x b. No local minimum or maximum c. Concave up for x > 0 , concave down for x < 0 d. Inflection point at x = 0

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[T] f ( x ) = ( x 2 ) 2 ( x 4 ) 2

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[T] f ( x ) = 1 1 x , x 1

a. Increasing for all x where defined b. No local minima or maxima c. Concave up for x < 1 ; concave down for x > 1 d. No inflection points in domain

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[T] f ( x ) = sin x x over x = [ −2 π , 2 π ] [ 2 π , 0 ) ( 0 , 2 π ]

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f ( x ) = sin ( x ) e x over x = [ π , π ]

a. Increasing over π 4 < x < 3 π 4 , decreasing over x > 3 π 4 , x < π 4 b. Minimum at x = π 4 , maximum at x = 3 π 4 c. Concave up for π 2 < x < π 2 , concave down for x < π 2 , x > π 2 d. Infection points at x = ± π 2

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f ( x ) = ln x x , x > 0

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f ( x ) = 1 4 x + 1 x , x > 0

a. Increasing over x > 4 , decreasing over 0 < x < 4 b. Minimum at x = 4 c. Concave up for 0 < x < 8 2 3 , concave down for x > 8 2 3 d. Inflection point at x = 8 2 3

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f ( x ) = e x x , x 0

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For the following exercises, interpret the sentences in terms of f , f , and f .

The population is growing more slowly. Here f is the population.

f > 0 , f > 0 , f < 0

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A bike accelerates faster, but a car goes faster. Here f = Bike’s position minus Car’s position.

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The airplane lands smoothly. Here f is the plane’s altitude.

f > 0 , f < 0 , f < 0

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Stock prices are at their peak. Here f is the stock price.

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The economy is picking up speed. Here f is a measure of the economy, such as GDP.

f > 0 , f > 0 , f > 0

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For the following exercises, consider a third-degree polynomial f ( x ) , which has the properties f ( 1 ) = 0 , f ( 3 ) = 0 . Determine whether the following statements are true or false . Justify your answer.

f ( x ) = 0 for some 1 x 3

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f ( x ) = 0 for some 1 x 3

True, by the Mean Value Theorem

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There is no absolute maximum at x = 3

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If f ( x ) has three roots, then it has 1 inflection point.

True, examine derivative

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If f ( x ) has one inflection point, then it has three real roots.

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Practice Key Terms 7

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Source:  OpenStax, Calculus volume 1. OpenStax CNX. Feb 05, 2016 Download for free at http://cnx.org/content/col11964/1.2
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