If under the root sign is a mathematical expression containing one or more variables values, try to simplify it and to take from under the radical. For example, if you need to subtract a square root from the expression 9*a2+9*b2+18*a*b, then the simplification will give a more comfortable set of two multipliers — 9*(a+b)2. The sign of the radical in this case can be removed after extracting the root of each factor: √(9*a2+9*b2+18*a*b) = √(9*(a+b)2) = 3*(a+b). Then use the obtained expression in a subtraction operation instead of the original square root.
If under the radical sign is the numerical value, the most simple way of solving the problem is to calculate the value of the root with subsequent subtraction of the obtained result. Having access to the Internet, make it very easy, even no need to make any calculations. Go, for example, on the website of the search engine Google and in the query box, type the desired mathematical operation. For example, if you want to subtract from the number 5831 square root of the 563, then enter "5831 — sqrt 563". In this entry, the abbreviation of the name of the square root (SQuare RooT) replaces the sign of the radical. Built-in search engine calculator will calculate and display the result even before clicking send request to the server: 5 831 — sqrt(563) = 5 807,27238.
Use the computing facilities of the operating system of your computer if access to the Internet. The easiest way in this case to use a program that simulates a basic calculator. In Windows it can run through the main menu by clicking "start" — a link is placed in its section "All programs". After opening the program dial the number from which to subtract the root, and then click M+ the calculator interface — so you put this value into its memory. Then enter the number from which to extract the root, and click the button with the icon of a radical (second from top in the right-most column), the calculator will display the calculated value. Press M-to subtract from the placed in the memory number of the value, and then use the MR button to let the app show the result. The number that the calculator will display, and will be the result of subtracting the square root.