1) 15сх+2су-сху-30с=с(15х+2у-ху-30)=с*(х*(15-у)+2(у-15))=с*(-х+2)*(у-15))
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2)35а^2-42аb+10a^2b-12ab^2=a*(35a-42b+10ab-12b^2)=a*(7(5a-6b)+2b*(5a-6b))=a*(7+2b)*(5a-6b)
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3)x^3+x^2y+x^2+xy=x*(x^2+xy+x+y)=x*(x*(x+y)+x+y)=x*(x+1)*(x+y)
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4)mn^4-n^4+mn^3-n^3=n^3*(mn-n+m-1)=n^3(m*(n+1)-(n+1))=n^3*(m-1)*(n+1)