3lg2-lg5=

3lg2-lg5= (lg2)³+(lg5)³+3lg2×lg5=? (lg2)³+(lg5)³+3lg2*lg5= lg2*lg2+lg5-lg2=? 3lg2+3lg5=? (lg2)^3+(lg5)^2= (lg2)^3+(lg5)^3+lg5*lg8=(lg2+lg5)[(lg2)^2-lg2*lg5+(lg5)^2]+lg5*lg2^3=1[(lg2)^2-lg2*lg5+(lg5)^2]+3lg5*lg2=(lg2)^2+(lg5)^2+2lg5*lg2=(lg2+lg5)^2=1网上看了看答案,可是第一步没有看懂.求得出第一步的过程, (lg2)x(lg2)x(lg2)+(lg5)^3+3xlg2xlg5=? lg2+lg5=?1-lg2=?1-lg5=?2lg5+2/3lg8+lg5*lg20+(lg2)2=? lg2(lg5-lg2)-lg5(lg5+3lg2)等于 (lg5)^2+lg5.lg2= (lg2)^3+(lg5)^3+3*lg2*lg5 (lg2)³+(lg5)³+3lg2×lg5 (lg2)^2+lg2*lg5+(lg5)^2= lg2*lg2+lg20*lg5=? lg2-lg5/lg4-lg5=2lg2-1/3lg2-1 为什么? 对数lg2*lg5=?2lg（5）+2/3 lg8+lg5*lg20+lg2 =lg5^2+lg8^(2/3)+lg5*(lg4+lg5)+lg2 =lg100+lg5+2lg2*lg5+lg2 =2+(lg5+lg2) =2+1 =3 第二个等号lg5*(lg4+lg5)为什么=lg5+2lg2*lg5 lg5^2+lg8^2/3+lg5*lg20+(lg2)^2=?