Look at the number as separate from the rest of the expression. 20=4*5 and 4 is a perfect square with square root=2. So the square root of 20=square root of 4 times the square root of 5. Square root of the variable x is found by dividing its exponent, or power, by 2, so 3 becomes 3/2 and the whole expression reduces to 2x^(3/2)sqrt(5).