This is a variation on the rules for multiplying powers, xaya = (xy)a. In the case of square roots, a=1/2. That is to say (√x)(√y) = √(xy).
It is very simple to multiply square roots in mathematics. When you are given with two square root numbers. And you have to multiply them. You just have to multiply the numbers with a common square root.
Multiply SQRT 4 and SQRT 10
SQRT 4 and SQRT 10
SQRT 4 X SQRT 10
SQRT (4 X 10)
SQRT 40 is the required answer.