If the midpoint of a chord of the ellipse x29 + y24 = 1 is ( 2, 4/3), and the length of the chord is 2 3, then is:
- 26
- 18
- 22
- 20
Answer
(3) 22
Solution
Chord with midpoint (x1, y1): T = S1
2x9 + (4/3)y4 = 29 + 16/94
2x9 + y3 = 23
2x + 3y = 6
Put y = 6 - 2x3 in 4x2 + 9y2 = 36:
4x2 + (6 - 2x)2 = 36
6x2 - 12 2x = 0 x = 0 or x = 2 2
End points (0, 2) and (2 2, 23 )
Length = (2 2)2 + ( 43 )2 = 8 + 169 = 883 = 2 223
= 22
Answer: (3)