lg5平方+2/3lg8+lg5乘以lg20+(lg2）平方
=2lg5+2lg2+lg5乘以（1+lg2）+(lg2）平方
=2+lg5+lg5*lg2+(lg2）平方
=2+lg5+(lg5+lg2)*lg2
=2+lg5+lg2
=2+1
=3