Let T be a tree of order n. Show that the size of the complement of T (T bar) is the same as the size of K(n-1)
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If $\displaystyle T$ is a tree with $\displaystyle n$ vertices the you know that $\displaystyle T$ has $\displaystyle n-1$ edges.
The complement $\displaystyle \overline{T}$ has $\displaystyle \binom{n}{2}-(n-1)$ edges.
The graph $\displaystyle K_{n-1}$ has $\displaystyle \binom{n-1}{2}$ edges.