Let ABCD be a trapezium whose vertices lie on the parabola y2 = 4x. Let the sides AD and BC of the trapezium be parallel to y-axis. If the diagonal AC is of length 254 and it passes through the point (1, 0), then the area of ABCD is
- 758
- 1258
- 252
- 754
Answer
(4) 754
Solution
(1, 0) is the focus of y2 = 4x (a = 1), so AC is a focal chord.
Let A = (t2, 2t); then C = ( 1t2, - 2t ) and length of focal chord = (t + 1t )2
(t + 1t )2 = 254 t + 1t = 52 t = 2 (or 12)
A = (4, 4), C = ( 14, -1 )
AD y-axis D = (4, -4); BC y-axis B = ( 14, 1 )
Parallel sides: AD = 8, BC = 2; distance between them = 4 - 14 = 154
Area = 12(8 + 2) 154 = 754
Answer: (4)