1.x²+x+4分之1
=x²+x+(1/2)^2
=(x+1/2)^2
2.-x²+4x-4
=-(x²-4x+2^2)
=-(x-2)^2
3.(a+b)²-18(a+b)+81
= (a+b)²-2*9(a+b)+9^2
=(a+b-9)^2
4.(m-2n)²-2(2n-m)(m+n) +(m+n)²
=(m-2n-(m+n))^2
=(-3n)^2
=9n^2
很高兴为您解答,希望对你有所帮助!
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