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Question

The equation of the tangents to the circle x2+y2=a2, which makes a triangle of area a2 sq. units with coordinate axes, is/are

A
x+y=a2
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B
xy=a2
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C
2x+3y=2a3
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D
2x3y=2a3
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Solution

The correct options are
A x+y=a2
B xy=a2
Let the tangent be of form xx1+yy1=1
and area of triangle formed by coordinate axes is:
12x1y1=a2 (1)
Rearranging equation of tangent, we get
xy1+yx1x1y1=0

Applying condition of tangency
∣ ∣ ∣x1y1x21+y21∣ ∣ ∣=a
x21+y21=x21y21a2

Using equation (1), we get
x21+(2a2x1)2=4a2t+4a4t=4a2 (t=x21)t24a2t+4a4=0t=2a2x21=2a2x1=±a2y1=±a2

Hence, the equation of the tangents are
x+y=a2x+y=a2xy=a2xy=a2

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