1 （a+b-3)(a-b-3) 2 (x+y+z)^2 3 1.234^2+0.766^2+2.468×0.766 4 2010^2

题目

1 （a+b-3)(a-b-3) 2 (x+y+z)^2 3 1.234^2+0.766^2+2.468×0.766 4 2010^2
1 （a+b-3)(a-b-3)
2 (x+y+z)^2
3 1.234^2+0.766^2+2.468×0.766
4 2010^2

答案

1 （a+b-3)(a-b-3)= [(a-3)+b][(a-3)-b]= (a-3)^2-b^2= a^2-6a+9-b^22 (x+y+z)^2 =(x+y)^2+z^2+2(x+y)z=x^2+y^2+2xy+z^2+2xz+2yz3 1.234^2+0.766^2+2.468×0.766 =1.234^2+0.766^2+2×1.234×0.766 =(1.234+0.766)^2...