(a+b-3)*(a+b+3)怎么算?

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(a+b-3)*(a+b+3)怎么算?
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(a+b-3)*(a+b+3)怎么算?
(a+b-3)*(a+b+3)怎么算?

(a+b-3)*(a+b+3)怎么算?
把a+b看成一项~
(a+b-3)*(a+b+3)=(a+b)^2-9=a^2+b^2+2ab-9

(a+b-3)*(a+b+3)
=[(a+b)-3][(a+b)+3]
=(a+b)^2-9
=a^2+2ab+b^2-9

(a+b-3)*(a+b+3)
=[(a+b)+3][(a+b)-3]
=(a+b)^2-9
=a^2+2ab+b^2-9

(a+b-3)*(a+b+3)=(a+b)²-3²=a²+2ab+b²-9

(a+b-3)*(a+b+3)
=(a+b)^2-3^2
=a^2+2ab+b^2-9