Calculus 1 : Differential Functions

Study concepts, example questions & explanations for Calculus 1

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Example Questions

Example Question #191 : Differential Functions

What is the first derivative of s(x) = 2sin(sin(x))?

Possible Answers:

ln(2) * 2sin(sin(x))  * cos(sin(x)) * cos(x)

None of the other answers

2cos(x)sin(x)

2cos(sin(x)) * cos(x)

ln(2) * 2cos(sin(x)) * cos(x)

Correct answer:

ln(2) * 2sin(sin(x))  * cos(sin(x)) * cos(x)

Explanation:

We must carefully parse this function in order to apply the chain rule correctly. Let us make the following substitutions:

f(x) = 2x

g(x) = sin(sin(x))

s(x) = f(g(x)) = 2sin(sin(x))

According to the chain rule, we know that s'(x)  = f'(g(x)) * g'(x)

f'(g(x)) = ln(2) * 2sin(sin(x))

g'(x) = cos(sin(x)) * cos(x)

Therefore, s'(x) = ln(2) * 2sin(sin(x))  * cos(sin(x)) * cos(x)

Example Question #1 : Other Differential Functions

What is the first derivative of f(x) = sin2(x) – sin(x)cos(x)?

Possible Answers:

2sin(x)cos(x) – 1

sin2(x) – 2sin(x)cos(x) – cos2(x)

2sin(x)cos(x) + 1

2sin(x)cos(x) + cos2(x) + sin2(x)

2sin(x)cos(x) – cos2(x) + sin2(x)

Correct answer:

2sin(x)cos(x) – cos2(x) + sin2(x)

Explanation:

Consider each of the elements in isolation:

sin2(x) can be differentiated using the chain rule.

Step 1: 2(sin(x))

Step 2: take the derivative of sin(x): cos(x)

Therefore, d/dx (sin2(x)) = 2sin(x)cos(x)

sin(x)cos(x) can be differentiated by the product rule:

cos(x)cos(x) + sin(x) * –sin(x) = cos2(x) – sin2(x)

Combine these:

2sin(x)cos(x) – (cos2(x) – sin2(x)) = 2sin(x)cos(x) – cos2(x) + sin2(x)

Example Question #2 : How To Find Differential Functions

What is the first derivative of f(x) = sin(x)ln(cos(x))?

Possible Answers:

cos(x)ln(cos(x)) + tan(x)sin(x)

cos(x)ln(cos(x)) – tan(x)sin(x)

None of the other answers

cos(x)ln(sin(x)) – sin2(x)

cos(x)ln(cos(x)) – tan(x)csc(x)

Correct answer:

cos(x)ln(cos(x)) – tan(x)sin(x)

Explanation:

This is a mixture of the product rule and the chain rule:

The first term of the product rule is: cos(x)ln(cos(x))

The second term will have sin(x) but will include the differentiation of the ln(cos(x)), which will require the chain rule:

sin(x) * (1/cos(x)) * (–sin(x)) = –sin2(x)/cos(x)

Combining both we get:

cos(x)ln(cos(x)) – sin2(x)/cos(x)

Now, note that none of the answers are the same as this ;however, we can make an alteration:

sin(x)/cos(x) is the same as tan(x)

Therefore, the answer is: cos(x)ln(cos(x)) – tan(x)sin(x)

Example Question #2 : Other Differential Functions

What is the first derivative of f(x) = sin(cos(tan(sin(x))))

Possible Answers:

sin(sin(tan(sin(x)))) * tan(sin(x))cos(x) * sin(sec2(sin(x)))

–cos(cos(tan(sin(x)))) * sec2(sin(x))cos(x) * sin(tan(sin(x)))

None of the other answers

cos(cos(tan(sin(x))))) * cos(tan(sin(x)))

cos(cos(tan(sin(x))))

Correct answer:

–cos(cos(tan(sin(x)))) * sec2(sin(x))cos(x) * sin(tan(sin(x)))

Explanation:

Okay, don't be overwhelmed.  Take this chain rule one step at a time:

Step 1: Do the sine...

cos(cos(tan(sin(x))))

Step 2: Do the cosine . . .

–sin(tan(sin(x)))

Step 3: do the tangent . . . this is the simple chain rule, so diffentiate the argument as well

sec2(sin(x))cos(x)

Step 4: Multiply them together:

–cos(cos(tan(sin(x)))) * sec2(sin(x))cos(x) * sin(tan(sin(x)))

Example Question #3 : How To Find Differential Functions

What is the first derivative of f(x) = sec(x2 + 4x)?

Possible Answers:

sec(2x + 4)tan(2x + 4)

2x * sec(x2 + 4x)tan(x2 + 4x) + 4sec(x2 + 4x)tan(x2 + 4x)

2x * tan(x2 + 4x) + 4tan(x2 + 4x)

2x * tan2(x2 + 4x) + 4tan2(x2 + 4x)

sec(x2 + 4x)tan(x2 + 4x)

Correct answer:

2x * sec(x2 + 4x)tan(x2 + 4x) + 4sec(x2 + 4x)tan(x2 + 4x)

Explanation:

This is a simple chain rule.  The derivative of the secant is secant * tangent; therefore:

f'(x) = sec(x2 + 4x) * tan(x2 + 4x) * (2x + 4)

Distribute everything to get your answer: 2x * sec(x2 + 4x)tan(x2 + 4x) + 4sec(x2 + 4x)tan(x2 + 4x)

Example Question #4 : Other Differential Functions

What is the first derivative of f(x) = cos4(x2)

Possible Answers:

–8x * sin(x2)cos3(x2)

4cos3(x2)

4cos3(x2)sin(x2)

4x * cos3(x2)

4x * sin(x2)cos3(x2)

Correct answer:

–8x * sin(x2)cos3(x2)

Explanation:

Consider this as a chain rule case.  Do each step:

Step 1: cos4

4cos3(x2)

Step 2: cos(x2); this can be treated like a normal case of the chain rule

–sin(x2) * 2x

Combining these, we get

–8x * sin(x2)cos3(x2)

Example Question #5 : Other Differential Functions

What is the first derivative of f(x) = (100/x2) + (50/x) – 200x2?

Possible Answers:

(14 + 4x + 3x4)/x3

(50 + 50x – 400x2)/x

–50(4 + x + 8x4)/x3

200x + 50 – 400x

None of the other answers

Correct answer:

–50(4 + x + 8x4)/x3

Explanation:

f(x) = (100/x2) + (50/x) – 200x2

First, rewrite the equation: 100x–2 + 50x–1 – 200x2

At this point, it is relatively easy to differentiate:

f'(x) = –2 * 100x–3 – 50x–2 – 400x = (–200/x3) – (50/x2) – 400x

Simplify by making x3 the common denominator:

(–200 – 50x – 400x4)/x3

Factor out the common –50 in the numerator to make things look nicer:

–50(4 + x + 8x4)/x3

Example Question #192 : Differential Functions

What is the first derivative of f(x) = 2x * ln(sin(x))?

Possible Answers:

2(ln(sin(x)) + x * tan(x))

2(ln(sin(x)) + x * cot(x))

2ln(sin(x))/cos(x)

2tan(x)

None of the other answers

Correct answer:

2(ln(sin(x)) + x * cot(x))

Explanation:

f(x) = 2x * ln(sin(x))

Here, we have a product rule with a chain rule.

The derivative of ln(sin(x)) = (1/sin(x)) * cos(x). Note that this is cot(x).

Therefore, our full derivative is:

f'(x) = 2ln(sin(x)) + 2x * cot(x) = 2(ln(sin(x)) + x * cot(x))

Example Question #12 : Other Differential Functions

What is the first derivative of f(x) = sin4(x) – cos3(x)?

Possible Answers:

4sin3(x) + 3cos2(x)

sin4(x)cos(x) + cos3(x)sin(x)

sin(x) + 1

4sin3(x)cos(x) + 3cos2(x)sin(x)

4sin3(x)cos(x) – 3cos2(x)sin(x)

Correct answer:

4sin3(x)cos(x) + 3cos2(x)sin(x)

Explanation:

f(x) = sin4(x) – cos3(x)?

Treat these as chain rules:

The derivative of sin4(x) is therefore: 4sin3(x)cos(x)

The derivative of cos3(x) is therefore: 3cos2(x) * –sin(x) or –3cos2(x)sin(x)

This gives us 4sin3(x)cos(x) + 3cos2(x)sin(x), which really cannot be simplified any further.

Example Question #13 : Other Differential Functions

What is the the first derivative of f(x) = 2tan(x)?

Possible Answers:

cot(x) * ln(2) * 2tan(x)

sec2(x) * ln(2) * 2tan(x)

ln(2) * 2sec(x)tan(x)

ln(2) * 2tan(x)

sec(x) * tan(x) * ln(2) * 2tan(x)

Correct answer:

sec2(x) * ln(2) * 2tan(x)

Explanation:

This is a case of the chain rule.

Step 1: Deal with the exponential function

ln(2) * 2tan(x)

Step 2: Deal with the exponent

sec2(x)

Multiply them together to get your answer:

sec2(x) * ln(2) * 2tan(x)

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