Increasing and descreasing function question

In summary, the conversation discusses finding the intervals on which a function increases or decreases, as well as factoring trigonometric expressions. It also mentions the derivative of a function and trigonometric identities.
  • #1
appplejack
43
0

Homework Statement


I've got two questions
1.Find the intervals on which f increases and and the intervals on which f decreases.

f(x)= x-cosx, 0≤x≤2∏

2. Why is f(x) = -2sin2x - 2sinx = -2sinx (2cosx + 1)
How can you factor 2cosx from the function on the left side?

Homework Equations





The Attempt at a Solution


1.I get f '(x) = 1 + sinx, 0≤x≤2∏
The answer says that it increases on [0,2∏] but I don't get it.
 
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  • #2
hi appplejack! :smile:
appplejack said:
2. Why is f(x) = -2sin2x - 2sinx = -2sinx (2cosx + 1)
How can you factor 2cosx from the function on the left side?

learn your trigonometric identities

sin2x = 2sinxcosx :wink:
1.I get f '(x) = 1 + sinx, 0≤x≤2∏
The answer says that it increases on [0,2∏] but I don't get it.

1 + sinx is always ≥ 0, isn't it? :smile:
 
  • #3
Thanks for your help but I think I need to work on trig. Could you explain why 1 + sinx is always ≥ 0?
 
  • #4
draw it! :biggrin:
 
  • #5
I'm weak on trig. For 1 + sinx, does it shift the graph upward by 1 because y intercept is 1
when x=0? And the graph of sine goes up and down. That's why I doubt that the function increases all the time. I know that I'm wrong but I'm still wondering why.
 
  • #6
appplejack said:
And the graph of sine goes up and down. That's why I doubt that the function increases all the time.

1 + sinx is the derivative, it doesn't matter if it goes up and down, so long as it doesn't become negative :wink:
 

Related to Increasing and descreasing function question

1. What is an increasing function?

An increasing function is a mathematical function where the output values increase as the input values increase. In other words, as the independent variable increases, the dependent variable also increases.

2. How can I determine if a function is increasing or decreasing?

To determine if a function is increasing or decreasing, you can look at the graph of the function. If the graph is moving from left to right and going upwards, then the function is increasing. If the graph is moving from left to right and going downwards, then the function is decreasing.

3. What is a local maximum or minimum?

A local maximum or minimum is a point on the graph of a function where the function reaches its highest or lowest value in a specific interval. It is also known as a relative maximum or minimum, as it is only the highest or lowest point within a particular range.

4. Can a function be both increasing and decreasing?

No, a function cannot be both increasing and decreasing. A function can either be increasing, where the output values increase as the input values increase, or decreasing, where the output values decrease as the input values increase.

5. How can I find the intervals where a function is increasing or decreasing?

To find the intervals where a function is increasing or decreasing, you can use the first derivative test. If the first derivative of the function is positive, then the function is increasing. If the first derivative is negative, then the function is decreasing. The points where the first derivative is equal to zero are the local maximum or minimum points.

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