Question 635435
Rationalize the denominator. Assume that all expressions under radicals represent positive numbers. 
a√-√b over √a+√b
I assume you meant to write it this way:
√a-√b over √a+√b
=(√a-√b)/(√a+√b)
multiply top and bottom by (√a-√b) (conjugate of (√a+√b))
=(√a-√b)^2/ (√a-√b)*(√a+√b)
=(√a-√b)^2/ (a-b)