(1)(x+y)2+2(x+y)+1
=(x+y+1)²;
(2)-2xy-x2-y2
=-(x+y)²;
(3)3ax2+6axy+3ay2
=3a(x+y)²;
(4)m4-81n4
=(m²+9n²)(m-3n)(m+3n)
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(1)(x+y)2+2(x+y)+1
=[(x+y)+1]²
=(x+y+1)²
(2)-2xy-x2-y2
=-(x²+2xy+y²)
=-(x+y)²
(3)3ax2+6axy+3ay2
=3a(x²+2xy+y²)
=3a(x+y)²
(4)m4-81n4
=(m²+9n²)(m²-9n²)
=(m²+9n²)(m+3n)(m-3n)