If x2+y2=1 then the distance from the point x,y,1−x2−y2 to the origin is
1
-1
0
2
Distance from point x,y,1−x2−y2 to the origin
=(x−0)2+(y−0)2+1−x2−y2−02=x2+y2+1−x2−y2=1+1−(1) ∵x2+y2=1 given =1=1