Taiyuan city in 2005-2006 school year, the seventh grade, the third mathematical evaluation, the answer to the 26th question.
( 1)20x 20-9x 9 20x 20-8x 8 20x 20-7x7 20x 20-6x 6 20x 20-5x 5 20x 20-4x 4 20x 20-3x 3
20x 20-2 x2 20x 20- 1x 1 20x 20-0x 0
(2) (a+b)x(a-b)=axa-bxb