В
(x²-1)/(1-x)(1+x+x²) - x²/(x²+x+1)=(x²-1-x²+x³)/(1-x³)=(x³-1)/(1-x³)=-1
д
a/(a(a+3)+(a-8)/a+(7a²-3a-72)/a(a-3)(a+3)=(a²+3a+a³-9a-8a²+72+7a²-3a-72)/a(a²-9)=
=(a³-9a)/(a³-9a)=1
е
1)1/a+1/b=(b+a)/ab
2)2/(a+b)*(b+a)/ab=2/ab
3)1/a²+1/b²+2/ab=(b²+a²+2ab)/a²b²=(a+b)²/a²b²
4)(a+b)²/a²b² :(a+b)²/a²b²=1