Q. 125.0( 4 Votes )

The line 2x – y + 4 = 0 cuts the parabola y2 = 8x in P and Q. The mid - point of PQ is
A. (1, 2)

B. (1, - 2)

C. (- 1, 2)

D. (- 1, - 2)

Answer :

Given that the line 2x - y + 4 = 0 cuts the parabola y2 = 8x at P, Q. We need to find the midpoint of PQ.


Substituting y = 2x + 4 in the equation of parabola.


(2x + 4)2 = 8x


4x2 + 16x + 16 = 8x


4x2 + 8x + 16 = 0


x2 + 2x + 4 = 0


Let x1, x2 be the roots. Then, x1 + x2 = - 2


Now substituting in the equation of the line we get,




y2 - 4y + 16 = 0


Let y1, y2 be the roots. Then, y1 + y2 = 4


Let us assume P be (x1, y1) and Q be (x2, y2) and R be the midpoint of PQ.




R = (- 1, 2)


The correct option is C

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