Number of Common Tangents to Two Circles in Different Conditions
The equation ...
Question
The equation of the common tangent of the two touching circles, y2+x2−6x−12y+37=0 and x2+y2−6y+7=0 is
A
x+y−5=0
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B
x−y+5=0
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C
x−y−5=0
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D
x+y+5=0
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Solution
The correct option is Cx−y−5=0 Let S1≡x2+y2−6x−12y+37=0 and S2≡x2+y2−6y+7=0 The equation of common tangent of the two circles is S1−S2=0 ⇒x2+y2−6x−12y+37−(x2+y2−6y+7)=0 ⇒−6x+6y+30=0 ⇒x−y−5=0