SOLUTION: Please help me solve this equation: Evaluate the integral {{{ int ( sqrt( (1+x)/(1-x)) ) }}}

Algebra ->  Test -> SOLUTION: Please help me solve this equation: Evaluate the integral {{{ int ( sqrt( (1+x)/(1-x)) ) }}}      Log On


   



Question 356418: Please help me solve this equation:
Evaluate the integral +int+%28+sqrt%28+%281%2Bx%29%2F%281-x%29%29+%29+

Answer by jsmallt9(3758) About Me  (Show Source):
You can put this solution on YOUR website!
+int+%28+sqrt%28+%281%2Bx%29%2F%281-x%29%29%2C+dx+%29+
The problem as you posted it is an indefinite integral. So we will not be evaluating (coming up with a numberic value for) it.

The "trick" to a lot of integration problems is to use Algebra (and perhaps Trig) to transform the integral you have into one or more integrals which fit a pattern you know how to identify.
With our integral, I am going to start by multiplying the numerator and denominator so that the numerator is a perfect square:
+int+%28+sqrt%28+%28%281%2Bx%29%2F%281-x%29%29%28%281%2Bx%29%2F%281%2Bx%29%29%29%2C+dx+%29+
This simplifies as follows:
+int+%28+sqrt%28+%281%2Bx%29%5E2%2F%281-x%5E2%29+%29%2C+dx+%29+
Using a property of radicals, root%28a%2C+p%2Fq%29+=+root%28a%2C+p%29%2Froot%28a%2C+q%29, we can split this square root of a fraction into a fraction of square roots:
+int+%28+sqrt%28+%281%2Bx%29%5E2%29%2Fsqrt%281-x%5E2%29+%2C+dx+%29+
And the numerator simplifies:
+int+%28+%281%2Bx%29%2Fsqrt%281-x%5E2%29+%2C+dx+%29+
(From the original function we know that 1+x must be positive so we do not need to be concerned with +- issues on this square root.)
We can now split this into separate fractions:
+int+%28+1%2Fsqrt%281-x%5E2%29++%2B+x%2Fsqrt%281-x%5E2%29%2C+dx+%29
Now we can use a property of integrals to split this into two:
+int+%28+1%2Fsqrt%281-x%5E2%29%2C+dx%29++%2B+int+%28+x%2Fsqrt%281-x%5E2%29%2C+dx+%29
By doing this manipulation of the integral we now have two integrals in a form we should be able to solve. The first one is of the form int+%281%2Fsqrt%28a%5E2+-+u%5E2%29%2C+du%29 with u = x and a = 1. And the second one is of the form of int+%28u%2Fsqrt%28a%5E2-u%5E2%29%2C+du%29 with u = x and a = 1. (In your Calulus book there is probably a table of common forms. You should be able to find both of these in this table so you can see where the solution came from:
   -1
sin  %28x%2F1%29+%2B+C%5B1%5D+%2B+%28-sqrt%281%5E2+-+x%5E2%29%29+%2B+C%5B2%5D

Simplifying and combining the two constants of integration into one we get:
   -1
sin  %28x%29+%2B+%28-sqrt%281+-+x%5E2%29%29+%2B+C