Verified Answer :

konrad509

\(d=35\\ d=\frac{n(n-3)}{2}\\ d=\frac{n(n-3)}{2}\\35=\frac{n(n-3)}{2}\\ 70=n^2-3n\\ n^2-3n-70=0\\ n^2-10n+7n-70=0\\ n(n-10)+7(n-10)=0\\ (n+7)(n-10)=0\\ n=-7 \vee n=10\\\\ n=10\)


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