Question 653213
When dealing with square roots, you always want to think about the square numbers (1, 4, 9, 16, 25...) that are multiples of the number you're given.

In sqrt(90), we can think of sqrt(9*10).  9 is a square number.  Its square root is 3.

So, (sqrt(90))/(sqrt(10)) =(sqrt(9)*sqrt(10)) / (sqrt(10))

The sqrt(10) on top will cancel with the sqrt(10) on bottom, leaving just sqrt(9) on top.  Well, what's the square root of 9?

3!