FINDING CRITICAL NUMBERS OF A FUNCTION WORKSHEET

Find any critical numbers of the function.

Problem 1 :

f(x) = x3 - 3x2

Solution

Problem 2 :

g(x) = x4 - 4x2

Solution

Problem 3 :

g(t) = t√(4 - t), t < 3

Solution

Problem 4 :

f(x) = 4xx2 + 1

Solution

Problem 5 :

h(x) = sin2x + cos x

0 < x < 2π

Solution

Problem 6 :

f(θ) = 2 sec θ + tan θ 

0 < θ < 2π

Solution

Answer Key

1) Critical numbers are x = 0 and x = 2.

2)  Critical numbers are x = ±√2.

3)  Critical numbers are t = 8/3.

4)  Critical numbers are x = 1 or -1.

5)  Critical numbers is x = π/3, 5π/3.

6)  Critical numbers is θ = 7π/6, 11π/6.

Use Calculus to find the CRITICAL POINTS of each of the following functions:

Problem 1 :

y = x2 - 6x + 5

Solution

Problem 2 :

y = x3/(x2 - 1)

Solution

Problem 3 :

f(x) = csc x ; [-π, π]

Solution

Problem 4 :

f(x) = ex - x

Solution

Problem 5 :

f(x) = 6x5 + 33x4 - 30x3 + 100

Solution

Problem 6 :

f(x) = 4x3 - 9x2 - 12x + 3

Solution

Problem 7 :

f(x) = 2/(t2 - 4)

Solution

Problem 8 :

f(x) = (ln x)2

Solution

Problem 9 :

f(x) = 2 sin(x/2) where [-2π, 2π]

Solution

Problem 10 :

f(x) = x2 ln (x)

Solution

Problem 11 :

The first derivative of the function 𝑓 is given by

f'(x) = sin2x/9 - (2/9)

How many critical values does f on the open interval (0, 10) ?

Solution

Problem 12 :

If 𝑓 is a continuous, decreasing function on [0,10] with a critical point at (4, 2), which of the following statements must be false?

(A) 𝑓(10) is an absolute minimum of f on [0,10].

(B) 𝑓(4) is neither a relative maximum nor a relative minimum.

(C) 𝑓′(4) does not exist

(D) 𝑓′(4) = 0            (E) 𝑓'(4) < 0

Solution

Answer Key

1)  The curve will flatten at the x-coordinate 3. So, the critical number is x = 3.

2)  x = 0, -√3, √3

3)  x = -π/2, π/2

4)  x = 0

5)  critical points are x = 0, -5 and 3/5.

6)  critical numbers are x = 2 and -1/2

7)  critical number is x = 0.

8)  critical number is x = 1

9)   critical numbers are x = -π and π

10)  critical number is x = 1/√e.

11)  Number of x-intercepts is 1. So, number of critical numbers is 1.

02)  option E is false.

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