1.

If `3x^(2)+2lambda xy + 3y^(2)+(6-lambda)x+(2lambda-6)y-21=0` is the equation of a circle, then its radius isA. 1B. 3C. `2sqrt(2)`D. none of these

Answer» Correct Answer - B
We have,
`3x^(2)+2lambda xy + 3 y6(2)+(6-lambda)+(2lambda-6)y-21=0 " " ...(i)`
This equation will represent a circle, if
Coeff. of `xy=0rarr lambda = 0`
Putting `lambda=0` in (i), we obtain `x^(2)+y^(2)+2x-2y-7=0`
Clearly, it represents a circle of radius `= sqrt(1+1+7)=3`.


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