A. 20202021×20212020-20202020×20212021怎麼簡算等於一萬
20202021×20212020-20202020×20212021怎麼簡算等於一萬？
20202021×20212020-20202020×20212021
=（20202020+1）*20212020-20202020*（20212020+1）
=20202020*20212020+20212020-20202020*20212020-20202020
=20212020-20202020
=10000