Obtaining Centre and Radius of a Circle from General Equation of a Circle
If the two ci...
Question
If the two circles, x2+y2+2g1x+2f1y=0 and x2+y2+2g2x+2f2y=0 touches each other, then-
A
f1g1=f2g2
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B
f1g1=f2g2
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C
f1f2=g1g2
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D
None
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Solution
The correct option is Bf1g1=f2g2 C1C2=r1±r2 ⇒(g1−g2)2+(f1−f2)2=(√g21+f21±√g22+f22)2 ⇒−2g1g2−2f1f2=±2(√g21+f21.√g22+f22)2 ⇒g1f2−g2f1=0 ⇒g1g2=f1f2 Ans: B