Step 1: Place a bar over every pair of digits starting from the unit digit. If the number of digits in it is odd, then the leftmost single digit too will have a bar.Thus we have, 7 29.So 1st bar is on 29 and 2nd bar is on 7.  
Step 2 : Find the largest number whose square is less than or equal to the 1st number,here it is '7'. (2^{2} < 7< 3^{2}). Here the we take 2. Divide and get the remainder (3 in this case). 

Step 3: Bring down the number under the next bar (i.e., 29 in this case) to the right of the remainder. So the new dividend is 329.  
Step 4 : Add the divisor 2 and quotient 2 that gives us 4.  
Step 5 : Think of a largest number in fill in the blank in such a way that the product of a new divisor and this digit is equal to or less than 329(new dividend). In this case 47 × 7 = 329. As 47 × 7 = 329 so we choose the new digit as 7. Get the remainder. 

Step 6 : Since the remainder is 0 and no digits are left in the given number, ∴√729 = 27. 