volk077 (x^3-x)/(x+1)=x(x^2-1)/(x+1)=x(x-1)(x+1)/(x+1)=x(x-1)

(4/49a²+16/63ab+64/81b²)(2/7a-8/9b)=(2/7a+8/9b)^2*(2/7a-8\9b)
при a=14; b=9 
(2/7a+8/9b)^2*(2/7a-8\9b)=(2/7*14+8/9*9)^2*(2/7*14-8/9*9)=(4+8)^2*(4-8)=144*(-4)=-576