Question:

If the circles \( x^2+y^2-8x-6y+c=0 \) and \( x^2+y^2-2y+d=0 \) cut orthogonally, then \( c+d \) equals

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Use standard form \(x^2+y^2+2gx+2fy+c=0\).
Updated On: Apr 30, 2026
  • \(6\)
  • \(4\)
  • \(2\)
  • \(0\)
  • \(1\)
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The Correct Option is B

Solution and Explanation

Concept: Orthogonal circles condition: \[ 2(g_1g_2 + f_1f_2) = c_1 + c_2 \]

Step 1:
Compare equations. First circle: \[ g_1=-4, f_1=-3 \] Second: \[ g_2=0, f_2=-1 \]

Step 2:
Apply condition. \[ 2((-4)(0)+(-3)(-1)) = c+d \] \[ 2(3) = c+d \] \[ c+d=6 \]
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