what is the square root of 2.8 x 10 ^-13?

Good answer GoldenLeaf!

$${\sqrt{{\mathtt{2.8}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{-{\mathtt{13}}}}} = {\mathtt{0.000\: \!000\: \!529\: \!150\: \!26}}$$

I did this straight on the site calc using the "Math input=result" tab

Note this is an aprroximation.  It is an irrational number and cannot be written exactly in digits. 

I hope you don't mind me checking some of your answers..  I will do it less as your ability, and my confidence in it, grows.

A really small number.

 

Though, in all seriousness, first you take 2.8 and move its decimal to the left 13 spaces.

 

0.00000000000028 is the number from that process.

 

Then, simply take the root of that number.

 

0.000000529150262 is your final answer