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If the circle x^2+y^2+2ax+8y+16=0 touc...

If the circle `x^2+y^2+2ax+8y+16=0` touch `x-axis ,` then the value of `a` is `+-16` (b) `+-4` (c) `+-8` (d) `+-1`

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`x^2+y^2+2ax+8y+16=0`
`x^2+y^2+2gx+2fy+c=0`
radius`=sqrt(g^2+f^2-c)`
`4=sqrt(a^2+16-16)`
`a=1`.
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