a. x^2 + 2root7x +7 + (Y-root 11)^2 =11 b. x^2 -12x + 84 =-y^2 + 16y
b. x^2-12x=84 -y^2+16y. x^2-12x+(-12/2)^2+y^2-16y+(-16/2)^2 = -84+36+64. x^2-12x+36+y^2-16y+(-16/2)^2 = -84. x^2-12x+36+y^2-16y+64 = -84+36+64. (x-6)^2+(y-8)^2 = 16. C(6.8). r^2 = 16. r = 4.
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