A³-b³=? a-b=7 ab=-6
a³-b³=(a-b)(a²+ab+b²)=7*(a²+ab-3ab+3ab+b²)=7*(a²-2ab+b²+3ab)=
=7*((a-b)²+3ab)=7*(7²+3*(-6))=7*(49-18)=7*31=217.
Ответ: a³-b³=217.
1) -2ху^2•3х^3у^5=-6х^4у^7
2)(-4аb^3)^2=16а^2b^6
(n²-m²)/((√n-√m)²+2√mn)= (n²-m²)/(n-2√mn+m+2√mn)= (n²-m²)/(n+m)= (n-m)(n+m)/(n+m)= n-m