Engineering
Mathematics
Tangent and Normal to Circle
Question

If a tangent to the circle x2 + y2 = 1 intersects the coordinate axes at distinct points P and Q, then the locus of the mid-point of PQ is

x2 + y2 – 16x2y2 = 0

x2 + y2 – 2x2y2 = 0

x2 + y2 – 4x2y2 = 0

x2 + y2 – 2xy = 0

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Solution

Let the mid point be S (h, k)

∴ P(2h,0) and Q(0,2k) equation of

PQ:x2h+y2k=1

∵ PQ is tangent to circle at R (say)

∴QR=1⇒|−1(12h)2+(12k)2|=1

⇒14h2+14k2=1

⇒ x2 + y2 – 4x2y2 = 0