令a=lg2,b=lg5
则a+b=lg2+lg5=1
原式=a³+b³+3ab
=(a+b)(a²-ab+b²)+3ab
=a²-ab+b²+3ab
=a²+2ab+b²
=(a+b)²
=1有的答案上(lg2)^3+(lg5)^3 +3lg2*lg5这步直接变成这步(lg2+lg5)(lg2^2-lg2*lg5+lg5^2)+3lg2*lg5我不明白你可以说说么谢谢立方和