You can try to bruteforce it out and just increment by 0.01 maybe that will work out.
But the answer wouldnt be exact.
So u can try in for an approx val.

Then test it up. If the value you got. is squared is lesser than the main number of which you should find the square root then increment. But if the the square of the value increases take the previous number as the approximate square root. So you will only be missing the minutest details

I want to implement undo logic which deletes the last drawn shape. To test this logic i had cleared shapes list and redrawn all shapes but still last ...