Why is 20 square + 21 square = 1282?

To start out it's actually not.

20^2= 400

21^2= 441

400+441= 841

So the real answer to this question is actually 841 instead of 1282.

Ok I got th answer that was the right answer but I still don't understand but how did you get the answer?

you must have types something in wrong someplace. Are you sure it's suppost to be 20 and 21 to be squared?

Yes they are