pls answer question 97

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l e t B b e (x 1, y 1, z 1) D (l, 0, 0) i s m i d p o i n t o f B C s o C i s (2 l - x 1, - y 1, - z 1) F (0, 0, n) i s m i d p o i n t o f A B s o A w i l l b e (- x 1, - y 1, 2 n - z 1) m i d p o i n t o f A C w i l l b e (l - x 1, - y 1, n - z 1) b u t E i s (0, m, 0) s o x 1 = l, y 1 = - m, z 1 = n A = (- l, m, n) B = (l, - m, n) C = (l, m, - n) A B^{2} = 4 l^{2} + 4 m^{2} C B^{2} = 4 n^{2} + 4 m^{2} A C^{2} = 4 l^{2} + 4 n^{2} s u m m i n g t h e t h r e e, w e g e t A B^{2} + B C^{2} + A C^{2} = 8 (l^{2} + m^{2} + n^{2}) \frac{A B^{2} + B C^{2} + A C^{2}}{l^{2} + m^{2} + n^{2}} = 8

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