Solving Difficult Integral: Strategies & Tips

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In summary, the problem involves a double integral with an integrand of cosx*sqrt(3+(cosx)^2) dxdy. The x bounds are from arctan(y) to pi/4 and the y bounds are from 0 to 1. Converting to polar coordinates may help, but previous attempts at using parts and trig substitution were unsuccessful. The final solution involves a trig substitution and the use of parts, resulting in the integrand (-3*ArcSinh[Cos[x]/Sqrt[3]])/2 - (Cos[x]*Sqrt[3 + Cos[x]^2])/2.
  • #1
Vampire
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Homework Statement


The whole integral is a double integral, but I can't even perform the first integration.

The integrand is cosx*sqrt(3+(cosx)^2) dxdy
The x bounds are from arctan(y) to pi/4
the y bounds are from 0 to 1

Homework Equations


Converting rectangular to polar may help.

The Attempt at a Solution



I've tried parts, but it was a disaster. I also started converting it to polar, but that was also a disaster.
 
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  • #2
I switched dx and dy and the bounds.

The new y bounds are from 0 to tanx
The new x bounds are from 0 to pi/4

The resulting integrand after successfully integrating in terms of y is

-sinx*sqrt(3 + (cosx)^2) dx

It's a little nicer, but still ugly.

Putting the integrand into the mathematica online integrator, I get this:

(-3*ArcSinh[Cos[x]/Sqrt[3]])/2 - (Cos[x]*Sqrt[3 + Cos[x]^2])/2

How do I get here? I tried by starting with parts, but it doesn't get me far.
 
  • #3
Solved with trig substitution and then parts.
 

Related to Solving Difficult Integral: Strategies & Tips

1. What is an integral and why is it difficult to solve?

An integral is a mathematical concept that represents the area under a curve on a graph. It is difficult to solve because it requires knowledge of various integration techniques and the ability to manipulate complex mathematical expressions.

2. What are some common strategies for solving difficult integrals?

Some common strategies for solving difficult integrals include using substitution, integration by parts, trigonometric identities, and partial fractions. It is important to also simplify the integral as much as possible before attempting to solve it.

3. How do I know which integration technique to use for a particular integral?

The choice of integration technique depends on the form of the integral and the functions involved. It is important to identify patterns and similarities with previously solved integrals and choose the appropriate technique based on that. Practice and familiarity with different integration methods can also help in making this decision.

4. Are there any tips to make solving difficult integrals easier?

Yes, there are a few tips that can help in solving difficult integrals. These include simplifying the integral, using trigonometric identities and other algebraic manipulations, and breaking the integral into smaller, manageable parts. It is also important to check for symmetry or other properties that can make the integral easier to solve.

5. What are some common mistakes to avoid when solving difficult integrals?

One common mistake to avoid is forgetting to use the correct integration technique or not following the correct order of operations. It is also important to double-check the final answer and make sure it is simplified and in the proper form. Lastly, be careful when using trigonometric identities or other substitution methods, as mistakes in these can easily lead to incorrect solutions.

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