Finding Length of Curve with Y^3/15 + 5/4y

In summary, the conversation was about finding the length of a curve given by the equation x=y^3/15 + 5/4y on the interval 3<=y<=5. The attempt at a solution involved calculating (dy/dx)^2 and using the formula for arc length, but the resulting integral was incorrect. The correct formula for arc length is sqrt{1 + (dx/dy)^2} and the final simplified integral should be sqrt{(y^2/5 + 5/4y^2)^2} with the limits of integration from 3 to 5, resulting in the correct answer of 67/10.
  • #1
whatlifeforme
219
0

Homework Statement


find the length of the curve.


Homework Equations


x=y^3/15 + 5/4y on 3<=y<=5


The Attempt at a Solution


(dy/dx)^2 = Y^4/25 - 1/2 + 25/16y^4

integral (3,5) y^2/5 + 5/4y^2

however, i got the wrong answer. the answer is 67/10.
 
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  • #2
whatlifeforme said:

Homework Statement


find the length of the curve.

Homework Equations


x=y^3/15 + 5/4y on 3<=y<=5

Is that 5/(4y) or (5/4)y. If you don't use Latex, at least use parentheses.

The Attempt at a Solution


(dy/dx)^2 = Y^4/25 - 1/2 + 25/16y^4

That isn't (dy/dx)^2 although it may be (dx/dy)^2

integral (3,5) y^2/5 + 5/4y^2

however, i got the wrong answer. the answer is 67/10.

That isn't the right formula for arc length. You need$$
\sqrt{1 + \left(\frac {dx}{dy}\right) ^2}\, dy$$in the integrand.
 
  • #3
ok so thus far this should be correct.

L = integral (3,5) sqrt(1 + y^4/25 - 1/2 + 25/16y^4)

this could be further simplified to: sqrt (y^2/5 + 5/4y^2)^2 --->

y^3/15 - 5/4y ] (3 to 5)

the answer is : 67/10 which I'm not getting.
 
  • #4
edit: solved.
 

Related to Finding Length of Curve with Y^3/15 + 5/4y

1. What is the formula for finding the length of a curve with the equation Y^3/15 + 5/4y?

The formula for finding the length of a curve with the equation Y^3/15 + 5/4y is the arc length formula, which is given by L = ∫√(1 + (dy/dx)^2)dx.

2. How do I find the derivative of Y^3/15 + 5/4y?

To find the derivative of Y^3/15 + 5/4y, first rewrite the equation as (1/15)y^3 + (5/4)y. Then, use the power rule to find the derivative, which is given by dy/dx = (3/15)y^2 + (5/4).

3. Can this equation be solved using integration?

Yes, this equation can be solved using integration. The arc length formula involves integration in order to find the length of a curve.

4. What are the limits of integration for this equation?

The limits of integration for this equation depend on the given curve and the range of values for y. They can be determined by looking at the starting and ending points of the curve.

5. Is there a simpler way to find the length of a curve with this equation?

No, the arc length formula is the most accurate way to find the length of a curve with this equation. However, if the equation is in a simpler form, there may be other methods to find the length of the curve, such as using the Pythagorean theorem.

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