JEE MAIN - Mathematics (2014 (Offline) - No. 13)
Let $$a, b, c$$ and $$d$$ be non-zero numbers. If the point of intersection of the lines $$4ax + 2ay + c = 0$$ and $$5bx + 2by + d = 0$$ lies in the fourth quadrant and is equidistant from the two axes then :
$$3bc - 2ad = 0$$
$$3bc + 2ad = 0$$
$$2bc - 3ad = 0$$
$$2bc + 3ad = 0$$
Explanation
Since the point of intersection lies on fourth quadrant and equidistant from the two axes,
i.e., let the point be (k, $$-$$k) and this point satisfies the two equations of the given lines.
$$\therefore$$ 4ak $$-$$ 2ak + c = 0 ......... (1)
and 5bk $$-$$ 2bk + d = 0 ..... (2)
From (1) we get, $$k = {{ - c} \over {2a}}$$
Putting the value of k in (2) we get,
$$5b\left( { - {c \over {2a}}} \right) - 2b\left( { - {c \over {2a}}} \right) + d = 0$$
or, $$ - {{5bc} \over {2a}} + {{2bc} \over {2a}} + d = 0$$ or, $$ - {{3bc} \over {2a}} + d = 0$$
or, $$ - 3bc + 2ad = 0$$ or, $$3bc - 2ad = 0$$
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