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Circle(s) touching x-axis at a distance 3 from the origin and having an intercept of length `2sqrt7` on y-axis is (are)A. `x^(2)+y^(2)-6x+- 8y+9=0`B. `x^(2)+y^(2)-6x pm 7y+9=0`C. `x^(2)+y^(2)+6xpm 8y+9=0`D. `x^(2)+y^(2)-8x pm 6y+9=0` |
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Answer» Correct Answer - A Let the equation of the circle be `x^(2)+y^(2)+2gx+2fy+c=0`. It touches x-axis at a distance 3 from the origin. Therefore, `c=g^(2)` and the circle passes through `(pm3, 0)`. `:. 9 pm 6g +c=0` `rArr 9 pm 6g + g^(2)= 0 rArr (gpm 3)^(2)=0 rArr g=-3` `:. c=g^(2)rArr c=9` The circle cuts an intercept of length `2 sqrt(17)` on y-axis. `:. 2 sqrt(f^(2)-c)=2sqrt(7)rArr f^(2)-9=7rArr f = pm 4` Hence, the equations of the circles are `x^(2)+y^(2)-6xpm 8y+9=0` |
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