- #1

mathwurkz

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[tex]R[/tex] is the larger ion radius, [tex]r[/tex] is the smaller ion radius and [tex]l[/tex] is the cube length edge.

Now what I don't get is how the book comes up with this relationship.

[tex] 2R + 2r = \sqrt{3}\ l [/tex]

The second expression [tex] l = 2R [/tex], I understand since the two large ions are touching each other, their radius will make up the length of the cube edge. They substitute this equation in the other and solve for [tex]\frac{r}{R}[/tex] It's just that I don't understand where that first equation comes from.