а)х^3 -ху ^2 + 3у^2 - 3х^2=x(x^2-y^2)-3(x^2-y^2)=(x-y)(x+y)(x-3)
б) 8m^4-m^7=m^4(8-m^3)=m^4(2-m)(4+2m+m^2)
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