The circle $ x ^ 2 + y ^ 2 - 2kx - 2ky + k ^ 2 = 0$ touches the x-axis at P and y-axis at Q. What is PQ equal to?

What is the equation of the circle whose diameter is 10 cm and the equations of two of its diameters are $x+y=0$ and $x-y=0$?

A square is inscribed in a circle x ² + y ² + 2x + 2y + 1 = 0 and its sides are parallel to coordinate axes. Which one of the following is a vertex of the square?

The equation of a circle is 

(x² - 4x + 3) + (y² - 6y + 8) = 0

Which of the following statements are correct?

I. The end points of a diameter of the circle are at (1, 2) and (3, 4).

II. The end points of a diameter of the circle are at (1, 4) and (3, 2).

III. The end points of a diameter of the circle are at (2, 4) and (4, 2).

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