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If the two vertex coordinates a (- 4,0), B (4,0) of △ ABC and the perimeter of △ ABC are 18, then the trajectory equation of vertex C is___ ．
(1) A (- 4,0), B (4,0), perimeter 18, ab = 8, BC + AC = 10, ∵ 10 ＞ 8, the sum of distances from C to two fixed points is equal to the fixed value, the trajectory of C is an ellipse with a and B as the focus, ∵ 2A = 10, 2C = 8, ∵ B = 3, so the standard equation of ellipse is X225 + Y29 = 1 (Y ≠ 0). So the answer is: X225 + Y29 = 1 (Y ≠ 0)
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