(2)2x？ xy-y？

(3) a? b？ -ab-6

(4)6ab-2ac-3b？ +bc

2. (4)

3.( 1)-a？ -3ab+2b？

(2)5x？ +8x？ + 12x+ 15

4. 15

5.[(3m+4n)+(2m+5n)×(m+2n)]\2

=[(3m+4n)+2m？ +9mn+ 10n？ ]÷2

And then it's easy to forget

As shown in the figure, AB=a, P is a point on the straight line AB, and squares are made with AP and BP as sides respectively. 1, let AP=X, and find the sum of the areas of two squares s (using the algebraic expression containing x) (two small squares are small on the left and large on the right ~)

2. When X= 1\3 a, the sum of the areas of two squares is s1; When x= 1\2 a, the sum of the areas of two squares is S2. Compare the size of S 1 and S2. As shown in the figure, AB=a, P is a point on the straight line AB, and squares are made with AP and BP as sides respectively.

( 1).x？ +(a-x)×(a-x)

=x？ +a？ -ax-ax+x？

=2x？ +a？ -2ax

(2).2×( 1/3a)？ +a？ -2a× 1/3a

=7/9a？

2×( 1/2a)？ +a？ -2a× 1/2a

=a？

S 1>S2