（c/ab）² ·（-b/ac）^3 ÷ （-b/a）^4
=(c^2/a^2b^2) •(-b^3/a^3c^3)•(a^4/b^4)
=-1/(ab^3c)
（3-a²）/（a²+2a+1）+【1-（1/a+1）】÷【1+（1/a-1）】
=（3-a²）/（a²+2a+1）+a/(a+1)÷a/(a-1)
=（3-a²）/（a+1)²+(a-1)/(a+1)
=(3-a²+a²-1)/(a+1)²
=2/(a+1)²
1/（2-a）-【（a+2/a²-2a）-（a-1/a²-4a+4）】÷a -4/2a
=-1/(a-2)-(a-4)/a(a-2)²•2a/(a-4)
=-1/(a-2)-2/(a-2)²
=-a/(a-2)²