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The seventh grade exercises the answers to some questions in the second volume of the mathematics grading class.
12.( 1)=x？ +2xy+y？

=x？ -2xy+y？ +4xy

=(x-y)？ +4xy

=9? +4*5

=6 1

(2)a(a- 1)+(b-a？ )=-7

Answer? -a+b-a？ =-7

a-b=7

Answer? +b？ /2-ab

=a？ +b？ /2-2ab/2

=a？ -2ab+b？ /2

=(a-b)？ /2

=7? /2=49/2

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