A line touches the ellipse x2a2+y2b2=1 and the circle x2+y2=r2 Then the slope m of the common tangent is given by m2=
A
a2−r2b2−r2
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B
r2−b2a2−r2
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C
r2+b2a2−r2
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D
r2−2b2a2−2r2
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Solution
The correct option is Ar2−b2a2−r2 Let y=mx+c be the equation of line Since, it touches circle and ellipse Then c2=r2(1+m2)=a2m2+b2 Therefore, m2=r2−b2a2−r2