Trig sine substitution doesnt work

In summary, the conversation discusses different ways to integrate the expression \int_{0}^{1} \sqrt{1 + 4t^2} dt, including using trigonometric substitutions and substitutions involving hyperbolic functions. The participants also talk about making the problem simpler by factoring out a common factor and using a half-angle substitution. They also briefly mention that the limits of integration may change depending on the substitution used.
  • #1
stunner5000pt
1,463
3
how would on integrate [tex] \int_{0}^{1} \sqrt{1 + 4t^2} dt [/tex]
trig sub sittution doesn't work since one doesn't get tan^2 +1 .

i tryed solving this with matematica and it yielded something with a sinh argument. I am not familiarwi the hyp sine substitution.
 
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  • #2
Use the sustitution [itex]2t = tan \theta[/itex]. Be prepared to integrate [itex]sec^3 \theta[/itex].

Regards,
George
 
  • #3
You may find that a substitution of t for sinh(theta)/2 will assist. And then you might find it useful to know how to write cosh(theta) in terms of exponentials.

Lots of ways to skin a small furry critter.

Carl
 
  • #4
to make things appear simpler factor out the 4, then make the proper trig substitution; if you still don't get it, you've definitely got some more studying to do.
 
  • #5
CarlB said:
Lots of ways to skin a small furry critter.
Carl

AbsolutelY!

Another way is to make the substitution [itex]2t = sinh x[/itex], and then to make a "half-angle" substitution for [itex]cosh^{2} x[/itex].

Regards,
George
 
  • #6
would the limits of integration change in this process?
for t=0, theta = 0
for t =1 , theta = arctan 2
is that right?
 

FAQ: Trig sine substitution doesnt work

What is trig sine substitution and why doesn't it always work?

Trig sine substitution is a technique used in calculus to solve integrals involving trigonometric functions. It involves substituting the variable x with sinθ to simplify the integral. However, this method does not always work because the resulting integral may not be solvable using traditional methods.

When should I use trig sine substitution?

Trig sine substitution should be used when the integral involves a radical expression or a quadratic expression with a negative discriminant. In these cases, substituting x with sinθ can help simplify the integral and make it more manageable.

What are some common mistakes when using trig sine substitution?

One common mistake when using trig sine substitution is forgetting to convert the limits of integration from x to θ. It is also important to keep in mind that the resulting integral must be converted back to the original variable x before evaluating the integral.

Are there other substitution methods for solving trigonometric integrals?

Yes, there are other substitution methods such as trig cosine substitution and trig tangent substitution. These methods can be used when the integral involves cosθ or tanθ, respectively. It is important to choose the appropriate substitution method based on the trigonometric function in the integral.

Can I always use trig sine substitution to solve trigonometric integrals?

No, trig sine substitution does not work for all trigonometric integrals. It is important to identify the type of integral and choose the appropriate substitution method. Some integrals may require other techniques such as integration by parts or trigonometric identities.

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