Question

1.已知xy=3,x+y=7.(1).求x^2+xy+y^2；（2）求（x-y)^2的值.2.已知8x^m+5*y^2n

Answer 1

1,x^2+xy+y^2=(x+y)^2-xy,

（x-y)^2==(x+y)^2-4xy

xy=3,x+y=7,代入就是.

2,5*y^2n/(2xy^n）表达在具体点.按照原题写清楚点吧.

3,（m-1/2)^2+1/3*In-2I=0可知,m=0.5,n=2,即得多项式与2a*b^2的乘积等于2a^3*b^2-6a^2*b^3+4ab^2,可得为a-6ab+1

4,第一季度电a,水2a+40,计3a+40,第二季度电0.85a,2水（2a+40）*1.38,共计3.61a+55.2.