Derive Distance Formula In Space

Can you derive the distance formula in space?
I am talking about the distance formula for points in space in the form (x, y, z).

Thanks

 

d=sqrt((x[2]-x[1])^2+(y[2]-y[1])^2+(z[2]-z[1])^2 )

 

This is a popular formula. I know how to use the formula but how is it derived?

 

here is good link to answer your question

 

Cool. I forgot to search You Tube clips.