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TS EAMCET · Maths · Circle

The slope of a common tangent to the circles \(x^2+y^2=16\) and \((x-9)^2+y^2=16\) is

  1. A \(\frac{8}{\sqrt{13}}\)
  2. B \(\frac{4}{\sqrt{13}}\)
  3. C \(\frac{\sqrt{17}}{8}\)
  4. D \(\frac{8}{\sqrt{17}}\)
Verified Solution

Answer & Solution

Correct Answer

(D) \(\frac{8}{\sqrt{17}}\)

Step-by-step Solution

Detailed explanation

\(C_1(0,0), r_1=4\) \(C_2(9,0), r_2=4\) Tangent: \(mx-y+c=0\) \(\frac{|c|}{\sqrt{m^2+1}}=4 \Rightarrow c^2=16(m^2+1)\) \(\frac{|9m+c|}{\sqrt{m^2+1}}=4 \Rightarrow (9m+c)^2=16(m^2+1)\) \((9m+c)^2=c^2 \Rightarrow 9m+c=\pm c\) \(9m+c=c \Rightarrow m=0\) (Horizontal tangents)…
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