You have to use distance formula.
(-4,8) and (10,-8)
[tex]\sqrt{(10 - (-4))^{2} + ((-8) - 8)^{2} }[/tex]
just for sake of making it easier to explain, let's use this:
[ (10 + 4)^2 + (-8 - 8)^2 ]^(1/2)
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[ (10 + 4)^2 + (-8 - 8)^2 ]^(1/2)
= [ (14)^2 + (-16)^2 ]^(1/2)
= [196 + 256]^(1/2)
= (452)^(1/2) = [tex]\sqrt{452}[/tex]
= 21.2029...
rounding up to 21 units between those points
