Let S denote the locus of the point of intersection of the pair of lines 4x-3y=12 , 4 x+3 y=12, where varies over the set of non-zero real numbers. Let T be the tangent to S passing through the points (p,0) and (0,q), q>0, and parallel to the line 4x- 3 2y=0. Then the value of pq is
- -6 2
- -3 2
- -9 2
- -12 2
Answer
(1) -6 2
Solution
Eliminate : (4x-3y)(4x+3y)=144 x29- y216=1 (hyperbola, a2=9, b2=16).
Slope of T: m= 4 23.
Tangent: y=mx a2m2-b2=mx 32-16=mx 4; q>0 q=4.
p=- qm=- 4 34 2=- 3 2
pq=- 12 2=-6 2
Answer: (A)