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Question:

If the vertices of a hyperbola are at (-6,0) and (2,0) and one of its foci is at (7,0), then which one of the following points does not lie on this hyperbola?

(2√2, √5)

(4, √15)

(-8, 2√10)

(6, 5√2)

Solution:

Let the vertices of the hyperbola be A(-6, 0) and B(2, 0). The center of the hyperbola is the midpoint of AB, which is ((-6+2)/2, (0+0)/2) = (-2, 0).
Let the focus be F(7, 0). The distance between the center and a vertex is a = 2 - (-2) = 4. The distance between the center and a focus is c = 7 - (-2) = 9.
The relationship between a, b, and c in a hyperbola is c² = a² + b². Therefore, b² = c² - a² = 9² - 4² = 81 - 16 = 65.
The equation of the hyperbola with center (-2, 0) is:
(x + 2)²/a² - y²/b² = 1
(x + 2)²/16 - y²/65 = 1
Now let's check each point:

  1. (2√2, √5):
    ((2√2) + 2)²/16 - (√5)²/65 = (2√2 + 2)²/16 - 5/65 ≈ 0.88 - 0.077 ≈ 0.8 ≠ 1
  2. (4, √15):
    (4 + 2)²/16 - (√15)²/65 = 36/16 - 15/65 = 9/4 - 3/13 ≈ 2.25 - 0.23 ≈ 2 ≠ 1
  3. (-8, 2√10):
    (-8 + 2)²/16 - (2√10)²/65 = 36/16 - 40/65 = 9/4 - 8/13 ≈ 2.25 - 0.615 ≈ 1.63 ≠ 1
  4. (6, 5√2):
    (6 + 2)²/16 - (5√2)²/65 = 64/16 - 50/65 = 4 - 10/13 ≈ 4 - 0.77 ≈ 3.23 ≠ 1
    Based on these calculations, none of the points perfectly satisfy the equation of the hyperbola. There might be a calculation error in the original solution or the provided options. However, the closest point to satisfying the equation is (2√2, √5).