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The directrices of x²/25 + y²/9 = 1 are the lines:
Ax = ±25/4
Bx = ±5/4
Cx = ±16/5
Dx = ±9/4
Answer & Solution
Correct answer: A. x = ±25/4
Here c = 4, so the directrices are x = ±a/e = ±a²/c = ±25/4.
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