lg5的平方+2/3lg8+lg5乘以lg20+（lg2）的平方
=lg5²+2/3lg8+lg5×lg20+（lg2）²
=2lg5+2/3lg2³+lg5×lg(4×5)+（lg2）²
=2lg5+(2/3)×3lg2+lg5×(lg4+lg5)+（lg2）²
=2(lg5+lg2)+lg5×lg2²+(lg5)²+（lg2）²
=2lg(5×2)+2lg5×lg2+(lg5)²+（lg2）²
=2lg10+(lg5+lg2）²
=2+[lg(5×2)]²
=2+(lg10)²
=2+1²
=3