(1)(a+b)^2-(a-b)^2 (2)-4x^2+12xy-9y^2

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(1)(a+b)^2-(a-b)^2(2)-4x^2+12xy-9y^2(1)(a+b)^2-(a-b)^2(2)-4x^2+12xy-9y^2(1)(a+b)^2-(a-b)^2(2)-4x^2+1

(1)(a+b)^2-(a-b)^2 (2)-4x^2+12xy-9y^2
(1)(a+b)^2-(a-b)^2 (2)-4x^2+12xy-9y^2

(1)(a+b)^2-(a-b)^2 (2)-4x^2+12xy-9y^2
1、(a+b)^2-(a-b)^2=a^2+2ab+b^2-(a^2-2ab+b^2)=4ab
2、-4x^2+12xy-9y^2=-(4x^2-12xy+9y^2)=-((2x)^2-2*(2x)*(3y)+(3y)^2)=-(2x-3y)^2

1、(a+b)^2-(a-b)^2
=(a+b-a+b)(a+b+a-b)=2b*2a=4ab
2、-4x^2+12xy-9y^2
=-(2x-3y)^2

=a^2+2ab+b^2-a^2-b^2+2ab
=4ab