How do I make a post solved please

I know from using practical values this does happen but I don't understand were the extra B is cancelled out

I will try again with LaTex

THIS IS NOT CORRECT perhaps some could show me what is wrong

$\displaystyle frac\{\sqrt{AB}{B}$

I still can not work LaTex out ! . I have been trying for 5 hours !

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This was muy original question

Here is a paint jobby