a+b=3,则a²-b²+6b

a+b=3,则a²-b²+6b
a+b=3,则a²-b²+6b

a+b=3,则a²-b²+6b
a²-b²+6b
=(a+b)(a-b)+6b
把a+b=3代入上式
=3(a-b)+6b
=3a+3b
=3(a+b)
=9
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a²-b²+6b
=(a+b)(a-b)+6b
=3(a-b)+6b
=3a+3b
=3(a+b)
=9

a²-b²+6b
=(a+b)(a-b)+6b
=3(a-b)+6b
=3a-3b+6b
=3a+3b
=3(a+b)
=3*3
=9

把a改为3-b 然后得（3-b）平方-b平方+6b。请采纳