CircleHard
Question
If P = (x, y), F1 = (3,0), F2 = (-3,0) and 16x2 + 25y2 = 400 then PF1 + PF2 equals
Options
A.8
B.6
C.10
D.12
Solution
Given, 16x2 + 25y2 = 400 (given)
⇒
Here, a2 = 25,b2 = 16
But b2 = a2 (1- e2)
⇒ 16 = 25(1- e2) ⇒
⇒
Now, foci of the ellipse are (±ae,0) ≡ (± 3,0).
we have,
⇒ a = 5
Now, PF1 + PF2 = major axis = 2a
= 2 × 5 = 10
Therefore, (c) is the answer.
⇒
Here, a2 = 25,b2 = 16
But b2 = a2 (1- e2)
⇒ 16 = 25(1- e2) ⇒
⇒
Now, foci of the ellipse are (±ae,0) ≡ (± 3,0).
we have,
⇒ a = 5
Now, PF1 + PF2 = major axis = 2a
= 2 × 5 = 10
Therefore, (c) is the answer.
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