Circle(s) touching x-axis at a distance 3 from the origin and having an intercept of length 27 on y-axis, is (are)
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a
x2+y2−6x±8y+9=0
b
x2+y2−6x±7y+9=0
c
x2+y2+6x±8y+9=0
d
x2+y2−8x±6y+9=0
answer is A.
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Detailed Solution
Let the equation of the circle be x2+y2+2gx+2fy+c=0. It touches x-axis at a distance 3 from the origin. Therefore, c=g2 and the circle passes through (±3, 0).∴ 9±6g+c=0⇒ 9±6g+g2=0⇒(g±3)2=0⇒g=−3∴ c=g2⇒c=9The circle cuts an intercept of length 27 on y-axis.∴ 2f2−c=27⇒f2−9=7⇒f=±4Hence, the equations of the circles are x2+y2−6x±8y+9=0