Question

The general form of the equation of a circle is x2 + y2 + 42x + 38y − 47 = 0. The equation of this circle in standard form is (x + 21)^2 + (y + 19)^2 = 849 .

The center of the circle is at the point A(-19, -21) B(-21, -19) C(19, 21) D(21, 19) , and its radius is A. 127^(1/2) B. 849^(1/2) C. 851^(1/2) D. 47 units.
The general form of the equation of a circle that has the same radius as the above circle is A. x^2 + y^2 + 60x + 14y + 98 = 0 B. x^2 + y^2 + 44x - 44y + 117 = 0 C. x^2 + y^2 - 38x + 42y + 74 = 0 D. x^2 + y^2 - 50x - 30y + 1 = 0 .           Someone please help with those 3 multiple choice ones.

Answer 1

for the center of this circle the right choice will be choice B. (-21,-19)

and its radius sqrt849 = 849^(1/2) so choice B. is right for this too

hope this will help you