I'd really like to know your thought process as to how to begin solving this problem, whether any substitution or any special technique, such as integration by parts, etc. were involved.
Thanks again!
Main Topics
Browse All TopicsIntegrate sqrt((1-x)/x)dx
I think I tried everything and I have spent more than an hour now. :(
Please help.
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Well, I've been unable to completely solve this so far; but, it would seem that at least integrating by parts initially is the way forward.
Letting u=sqrt((1-x)/x), and v'=1, results in:
uv - Integral{ vu' }dx = x sqrt[(1-x)/x] + 1/2 Integral{ 1/x sqrt[x/(1-x)] }dx
From that, you can see that the left term "x sqrt[(1-x)/x]" is in the final answer (see ozo's solution), and some of the other terms can be found from the integral on the right; for example, x/(1-x) = 1 - 1/(x-1)..
But, like I say, I'm so far unable to get much further than this.
[Awaiting ozo's next visit...]
I don't like ozo's answer because it contains sqrt(x-1), which complicates matters when x < 0 and everything could potentially be real-valued. In other words, I'd prefer to see a result where there weren't any imaginary intermediate values when x < 0 or x > 1. However, the Wolfram Integrator (http://integrals.wolfram.
log(ai+b) = log(sqrt(a^2+b^2)) + i*atan2(a,b)
Assuming 0 < x < 1
sqrt(x-1) = i*sqrt(1-x)
a=sqrt(1-x), b = sqrt(x)
log(sqrt(1-x)*i + sqrt(x)) = log(sqrt(1-x + x)) + i*theta
= log(sqrt(1)) + i*theta
= i*theta,
So it looks like the log term is purely imaginary when 0 < x < 1, so multiplying it by i makes it real.
given that 0 < x < 1,
theta = asin(sqrt(1-x) / sqrt(sqrt(1-x)^2 + sqrt(x)^2))
= asin(sqrt(1-x) / sqrt(1 - x + x))
= asin(sqrt(1-x))
So, it looks like we can replace the i*log with asin(sqrt(1-x))
integral = x*sqrt((1-x)/x) - asin(sqrt(1-x))
Let's take the derivitive and see what we get.
d{sqrt((1-x)/x)) = d{sqrt(1-x) / sqrt(x) } =
(sqrt(x)*(-0.5/sqrt(1-x)) - sqrt(1-x)*(0.5/sqrt(x))) / x =
multiply num and denom by sqrt(x)*sqrt(1-x)
(x*(-0.5) - (1-x)*(0.5))/(x*sqrt(x)*sq
(-x/2 - 1/2 + x/2) =
1/(2*x*sqrt(x)*sqrt(1-x))
d{x*sqrt((1-x)/x)} = 1/(2*sqrt(x)*sqrt(1-x)) + sqrt((1-x)/x)
d{asin(f(x))} = f'(x) * 1/sqrt(1 - f(x)^2)
d{asin(sqrt(1-x))} = (-0.5/sqrt(1-x)) * 1/sqrt(1 - (1-x))
= (-0.5/sqrt(1-x)) / sqrt(x)
= - 1/(2*sqrt(x)*sqrt(1-x))
adding it all together:
d{x*sqrt((1-x)/x) - asin(sqrt(1-x))}
= 1/(2*sqrt(x)*sqrt(1-x)) + sqrt((1-x)/x) - 1/(2*sqrt(x)*sqrt(1-x))
= sqrt(1-x)/x
So I believe that shows that the integral of sqrt(1-x)/x is x*sqrt((1-x)/x) - asin(sqrt(1-x)) + C
hello
it is very easy: look!
integral : ( x^2 - 2*x +1 ) / (x^2) dx
now divide ( x^2 - 2*x +1 ) to (x^2) . so the question will have another form:
integral : [ 1 - 2/x + 1/(x^2) ] dx
well, now we can easily solve it:
equals with : x - 2*Ln(x) - a/x + Constant
or
equals with : x - Ln(x^2) - a/x + Constant
the both are correct, no difference. Regards!
hello
it is very easy: look!
integral : ( x^2 - 2*x +1 ) / (x^2) dx
now divide ( x^2 - 2*x +1 ) to (x^2) . so the question will have another form:
integral : [ 1 - 2/x + 1/(x^2) ] dx
well, now we can easily solve it:
equals with : x - 2*Ln(x) - a/x + Constant
or
equals with : x - Ln(x^2) - a/x + Constant
the both are correct, no difference. Regards!
Hi mymaddy,
Put x = sin? t
dx = 2 sin t cos t dt
sqrt ( (1 - x) / x ) = sqrt ( (1 - sin? t) / sin? t )
= sqrt ( cot? t )
= cot t
So, sqrt ( (1 - x) / x ) dx = cot t * 2 sin t cos t = 2 cos? t
Integrating it, we get
t + cos t sin t
By back substitution, it comes out to be
= arcsin( sqrt(x) ) + sqrt(1 - x) * sqrt(x) + C
---
Harish
Business Accounts
Answer for Membership
by: ozoPosted on 2007-02-06 at 22:13:09ID: 18482865
sqrt((1-x)/x) (x-log(sqrt(x-1)+sqrt(x))s qrt(x/(x-1 ))