In the quadratic function x 2/a+y 2/b =1,when a = b >；; 0, you can get a circle. The radius of this circle = the square root of a.

Of course, when a=b= 1, it is also a circle with a radius of 1 (just a special case above).

When a>0, b>0, and A is not equal to B, an ellipse can be obtained. For example, a= 1 and b=2 are also ellipses.

So it is correct to make a condition that A is not equal to B in the title.

What you said that A is not equal to 1 and B is not equal to 1 is incorrect.

Analyze your conditions: take A = 2 and B = 2 as ellipses, but take a= 1.b=2 as circles and remove them.