ab=[2(1-lg2)]/3lg2怎么化简成lg2=2/(3ab+2)

已知a+b=lg2^2+lg2^5+2lg2*lg5,求3ab+a^3+b^3之值 3*(lg2)^2+3(1-lg2)*lg2+2(1-lg2)-lg2+9/2 2(lg2)2+lg2•lg5+(lg2)2-lg2+1=lg2（2lg lg2^2+lg2*lg5+lg5=lg2(lg2+lg5)+lg5 (lg2^2+1)(lg2)^2+1=? lg25+lg2*lg50+(lg2)^2+1=? lg5*(1+lg2)+(lg2)^2= 1/2(lg2)^2+1/2lg2*lg5+√1/4(lg2)^2-lg2+1=? 2(lg2)^2+(lg5)^2+3lg2lg5-lg2= [(lg2)^3+(lg5)^3-1]/[(lg2)^2+(lg5)^2-1]=多少 怎么算 (lg2)^3+(lg5)^2= lg5^2+2lg2-lg2^2=?