C No. 52, and D No. 73.
Then AB = √(12 2 + 5 2 ) = √169 = 13; AC = 21; AD = √(9 2 + 8 2 ) = √145 = 12+ (N.B. i.e. "between 12 and 13.") BC = √(16 2 + 12 2 ) = √400 = 20; BD = √(3 2 + 21 2 ) = √450 = 21+; CD = √(9 2 + 13
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APPENDIX.
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