Calculating the Area Under a Trig Graph

In summary, the conversation is about finding the area under the graph of a trigonometric function using approximating rectangles and right endpoints. The conversation also touches on the fundamental theorem of calculus and the use of different equations and intervals to simplify calculations. The expert summarizer provides information on the existence of formulas for sums of trigonometric functions and suggests using the geometric series to derive them. The conversation ends with the expert agreeing that changing the equation and interval is possible, but not necessarily easier.
  • #1
Miike012
1,009
0
Question: Find the area under the graph y = cos(x) from x = 0 to x = pi/2

Solution:

A = Lim ( ∏/(2n) * Ʃ cos( ∏i/(2n)) = ? Start: i = 0 and End: n = n
n → ∞

Just like there is a theorem for adding consecutive numbers... n(n + 1)/2..
Is there one for trig functions?
 
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  • #2
I don't know of any nice formula for that sum. (That doesn't mean there isn't one.) Are you studying approximating sums for integrals but don't have the fundamental theorem of calculus yet?
 
  • #3
I guess you can say that... The real question was ... estimate the area of cos(x) [0,pi/2] using 4 approximating rectangles and right endpoints..

That is easy so I wanted to try and solve for n rectangles..
 
  • #4
Miike012 said:
I guess you can say that... The real question was ... estimate the area of cos(x) [0,pi/2] using 4 approximating rectangles and right endpoints..

That is easy so I wanted to try and solve for n rectangles..

That's good that you found it so easy. That means you get the idea and that is what counts. There is a reason calculus books typically only do the limit thing for parabolas. Try that if for y = x2 if your book hasn't already done it for you. You will be able to calculate it.

Trying it for most functions will leave you with a sum that you can't evaluate in closed form, such as you have just experienced. That is why the fundamental theorem of calculus is so important.
 
  • #5
one more question...

Estimate the area under the graph of f(x) = 1 + x^2 from x = -1 to x = 2 using 6 rectangles and right end point.

Question:
Can I change the equation from 1 + x^2 to 1 + (x - 1)^2 and change the interval to x = 0 to x = 3 ??

This seems logical because technically it would be the same area.. and it is easier for me to break up into 6 rectangles.
 
  • #6
LCKurtz said:
I don't know of any nice formula for that sum. (That doesn't mean there isn't one.) Are you studying approximating sums for integrals but don't have the fundamental theorem of calculus yet?

Just for the record, there are formulas like that. See http://en.wikipedia.org/wiki/List_of_trigonometric_identities Look under "Other sums of trigonometric functions". You can derive them by summing the geometric series exp(i*a*k) and splitting into real and imaginary parts.
 
  • #7
Miike012 said:
one more question...

Estimate the area under the graph of f(x) = 1 + x^2 from x = -1 to x = 2 using 6 rectangles and right end point.

Question:
Can I change the equation from 1 + x^2 to 1 + (x - 1)^2 and change the interval to x = 0 to x = 3 ??

This seems logical because technically it would be the same area.. and it is easier for me to break up into 6 rectangles.

Yes you could, but I don't see why it is any easier.
 

1. How do you calculate the area under a trig graph?

To calculate the area under a trig graph, you need to use integration. The formula for finding the area under a curve is given by the integral of the function from the lower limit to the upper limit. For a trigonometric function, you would need to find the antiderivative and then evaluate the integral using the limits of integration.

2. What is the difference between calculating the area under a trig graph and a regular graph?

The main difference between calculating the area under a trig graph and a regular graph is that trigonometric functions have a periodic nature. This means that the area under one cycle of the function may be different from the area under another cycle. Therefore, when calculating the area under a trig graph, you need to consider the appropriate limits of integration to get an accurate result.

3. Can I use the same method to calculate the area under any trig graph?

Yes, you can use the same method of integration to calculate the area under any trig graph. However, the limits of integration may vary depending on the specific trig function and the interval over which you want to find the area. It is important to carefully choose the appropriate limits to get an accurate result.

4. Can I use the Riemann sum method to approximate the area under a trig graph?

Yes, the Riemann sum method can be used to approximate the area under a trig graph. However, since trigonometric functions are continuous, using a larger number of rectangles in the Riemann sum will result in a more accurate approximation of the area. It is recommended to use a computer or calculator to calculate the Riemann sum for a trig function with a large number of rectangles.

5. How can calculating the area under a trig graph be useful in real life?

Calculating the area under a trig graph can be useful in various real-life applications such as physics, engineering, and economics. For example, in physics, the area under a velocity-time graph represents the displacement of an object, and the area under an acceleration-time graph represents the change in velocity. In engineering, the area under a force-displacement graph can represent the work done by a force, and in economics, the area under a demand or supply curve can represent the consumer surplus or producer surplus, respectively.

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