（１）25x^2＋20x＋4=(5X)^2+2(5X)*2+2^2=(5X+2)^2
（２）-81x^2＋108x－36=-[(9X)^2-2(9X)*6+6^]=-(9X-6)^2=-9(3X-2)^2
（３）(3x－4)^2－4=(3X-4-2)(3X-4+2)=(3X-6)(3X-2)=3(X-2)(3X-2)
（４）-32X^2＋98y^2=2(49Y^2-16X^2)=2(7Y-4X)(7Y+4X)
（５）x^2－x=X(X-1)
（６）a^2＋b^2－2ab－c^2=(a-b)^2-c^2=(a-b-c)(a-b+c)
（７）(1＋xy)^2－(x－y)^2=(1+xy-x+y)(1+xy+x-y)
（８）9x^2－1＋(3x－1)^2=(3x-1)(3x+1)+(3x-1)^2=(3x-1)(3x+1+3x-1)
=6x(3x-1)
２.9x^2＋囗x＋4=(3x)^2+2(3x)*2+2^2..框框=正負12
3.4x^2－12xy＋9y^2－4x＋6y＋3＝(2x-3y)^2-2(2x-3y)+3=(-4)^2-2(-4)+3
=16+8+3=27
4.(x＋2y)^2－8xy=x^2+4xy+4y^2-8xy=x^2-4xy+4y^2=(x-2y)^2
(826＋2×263)^2－8×826×263＝(826-2×263)^2=(826-526)^2=300^2=90000
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