Q42 / 90 · JEE Main 2021 (27 Jul Shift 2) · Mathematics

Two sides of a parallelogram are along the lines 4x+5y=0 and 7x+2y=0 . If the equation of one of the diagonals of the parallelogram is 11x+7y=9, then other diagonal passes through the point:

  • A
    1,2
  • Correct answer
    B
    2,2
  • C
    2,1
  • D
    1,3

Solution

Both the lines 4x+5y=0,7x+2y=0 pass through origin.

Figure

D is the point of intersection of 4x+5y=0 & 11x+7y=9

So upon solving we get the coordinates of point D=53,-43

Also, point B is the point of intersection of 7x+2y=0 & 11x+7y=9

So, coordinates of point B=-23,73

The diagonals of parallelogram bisect each other, so the mid point of BD is

53-232,-43+732=12,12

The equation of diagonal AC is

y-0=12-012-0x-0 i.e., y=x

Therefore, the diagonal AC passes through 2,2.

Hence, the correct answer is option: 'B'.

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