1.4m-7n-2(m-2n) 2 -(x？ 2xy-y？ )+(5x？ -2xy-3y？ )

=4m-7n-2m+4n =-x？ +2xy+y？ +5x？ -2xy-3y？

=2m-3n =4x？ -2y？

two

1.2x？ y-(5xy？ -3x？ y)-x？

= 2x？ y-5xy？ +3x？ y-x？

=5x？ y-5xy？ -x？

=5xy(x-y) -x？

When x =- 1 and y = 1, the original formula = 5× (-1)×1(-1)) = 9.

2 .4B-A

=4(ab-2b？ -a？ )- (3b？ -2a？ )

=4ab-8b？ -4a？ - 3b？ +2a？

=﹣2a？ ﹣ 1 1b？ +4ab

When a=2 and b=-? When, the original formula =-2×2? - 1 1×(﹣? )? +4×2×﹙﹣? ﹚= ﹣8- 1 1× ﹙ 1/4)﹢4×2×? =﹣﹙27/4)

3.？ (x+y)-4(x-y)+3(x-y)-3/2(x+y)+(x-y)

= - (x+y)

When x+y=-4, the original formula =4.

three

1. Total cost = 20x+8y+20x+8x+2+60x+12y.

2. Perimeter = 2 | 3m+2n |+2 [3m+2n-m-n |]

=+2 ~ 3m+2n-m+n ~ 6m +4n in the north.

=+2 ~ 2m+3n ~ 6m +4n in the north.

=6m +4n +4m+6n

= 10m+ 10n

= 10﹙m+n﹚

3. New number: 10y+x Original number:10x+y.

Sum of new number and original number =10y+x+10x+y =1x+11y =1! X+Y！

The difference between the new number and the original number is =10y+x-|10x+y | =10y+x-10x-y = 9 | y-x |