Where is the Local Maximum for y = (8/5)sin(t) + (4/5)cos(t) - (9/5)e^(-t/2)?

In summary, the problem is to find the local maximum of the given function y=(8/5)sint + (4/5)cost - (9/5)e^(-t/2). The student has differentiated the function and found dy/dx, but since there is no x variable, it is assumed they meant dy/dt. However, there is no closed-form solution for finding the value of t when dy/dt=0, so numerical methods must be used. Plotting the function and its derivative can provide helpful insights. The original thread title was mis-named as it is not a differential equation, but a differentiation problem.
  • #1
cloveryeah
26
0

Homework Statement


y=(8/5)sint + (4/5) cost - (9/5)e^(-t/2)

find its local max

Homework Equations

The Attempt at a Solution


i have differentiated it and found out dy/dx,
in order to find the local max, i have to find out the value t when dy/dx=0
but i can't solve this equation
 
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  • #2
Local in what neighborhood? I don't see any x in the problem you posted, what is dy/dx?
Note that as t gets large, you can neglect the exponential term. Then you can easily solve the trigonometric equation.
 
  • #3
cloveryeah said:

Homework Statement


y=(8/5)sint + (4/5) cost - (9/5)e^(-t/2)

find its local max

Homework Equations

The Attempt at a Solution


i have differentiated it and found out dy/dx,
in order to find the local max, i have to find out the value t when dy/dx=0
but i can't solve this equation

Of course, dy/dx = 0 because your y does not contain any x variable. However, if you mean dy/dt then I agree, you have an "unsolvable" problem, in the sense that there will be no nice closed-from solution. However, you can use numerical methods.

In such cases, always start by plotting a graph of your function, to get a feel for what is happening. Plotting the derivative can be helpful, too.

BTW: your post is mis-named. You do not have a differential equation, you just have a given function that you want to differentiate.
 
  • #4
Ray Vickson said:
BTW: your post is mis-named. You do not have a differential equation, you just have a given function that you want to differentiate.
I changed the thread title...
 

Related to Where is the Local Maximum for y = (8/5)sin(t) + (4/5)cos(t) - (9/5)e^(-t/2)?

1. What is a local maximum value?

A local maximum value is a point on a graph or function where the value is higher than all surrounding points, but not necessarily the highest value on the entire graph. It is also known as a peak or crest.

2. How do you find the local maximum value of a function?

To find the local maximum value of a function, you can use the first or second derivative test. The first derivative test involves finding the critical points of the function and then checking the sign of the derivative at those points. If the derivative changes from positive to negative, then the point is a local maximum. The second derivative test involves finding the critical points and then evaluating the second derivative at those points. If the second derivative is negative, then the point is a local maximum.

3. What is the difference between a local maximum and a global maximum?

A local maximum is a point on a graph or function where the value is higher than all surrounding points, but not necessarily the highest value on the entire graph. A global maximum, on the other hand, is the highest value on the entire graph or function. In other words, a global maximum is also a local maximum, but a local maximum is not always a global maximum.

4. Can a function have more than one local maximum value?

Yes, a function can have more than one local maximum value. This occurs when the function has multiple peaks or crests. The number of local maximum values a function has is equal to the number of peaks or crests on the graph.

5. Why is finding the local maximum value important?

Finding the local maximum value is important because it allows us to identify the highest points on a graph or function. This can be useful in various real-world applications, such as determining the maximum profit in a business or the maximum temperature in a certain area. Additionally, understanding the behavior of a function at its local maximum values can provide insights into the overall behavior of the function.

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