Straight Line and Pair of Straight Lines 1 Question 63

63. Two sides of a rhombus ABCD are parallel to the lines y=x+2 and y=7x+3. If the diagonals of the rhombus intersect at the point (1,2) and the vertex A is on the Y-axis, find possible coordinates of A.

(1985,5M)

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Solution:

  1. Let the coordinates of A be (0,α). Since, the sides AB and AD are parallel to the lines y=x+2 and y=7x+3, respectively.

The diagonal AC is parallel to the bisector of the angle between these two lines. The equation of the bisectors are given by

xy+22=±7xy+3505(xy+2)=±(7xy+3)2x+4y7=0 and 12x6y+13=0.

Thus, the diagonals of the rhombus are parallel to the lines 2x+4y7=0 and 12x6y+13=0.

 Slope of AE=24 or 1262α10=12 or 2α10=2α=52 or α=0.

Hence, the coordinates are (0,5/2) or (0,0).



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