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AP EAMCET · Maths · Circle

If the angle between the circles \(x^2+y^2+2 x-4 y+1=0\) and \(x^2+y^2-4 x-2 y+c=0\) is \(\frac{\pi}{4}\), then \(c=\)

  1. A \(3\)
  2. B \(-13\)
  3. C -3 or 13
  4. D -31 or -3
Verified Solution

Answer & Solution

Correct Answer

(A) \(3\)

Step-by-step Solution

Detailed explanation

\(\begin{aligned} & \text { (a) } x^2+y^2+2 x-4 y+1=0 \\ & \therefore g_1=1, f_1=-2, c_1=1 \\ & x^2+y^2-4 x-2 y+c=0 \\ & \therefore g_1=-2, f_2=-1, c_2=\mathrm{c} \end{aligned}\) Now, angle between the circles is…