Press Ctrl + Shift + U , then type 221a , and hit Enter .
If you are using a laptop or a compact keyboard without a numeric keypad, the Character Map is your best friend. how to type square root on keyboard
If all else fails, or if you are working on a device with a limited interface (like a smart TV or a public computer), the easiest method is to simply copy the symbol from a web page. Press Ctrl + Shift + U , then type 221a , and hit Enter