Trong không gian $Oxyz$, mặt cầu tâm $I\left(2;-1;1\right)$, bán kính $R=2$ có phương trình là

	$\left(x+2\right)^2+\left(y-1\right)^2+\left(z+1\right)^2=2$
	$\left(x-2\right)^2+\left(y+1\right)^2+\left(z-1\right)^2=2$
	$\left(x+2\right)^2+\left(y-1\right)^2+\left(z+1\right)^2=4$
	$\left(x-2\right)^2+\left(y+1\right)^2+\left(z-1\right)^2=4$