1.原式=21（lg20/3+lg3）- lg7 + lg7 - lg4
=21lg20-2lg2
=21(2lg2+lg5)-2lg2
=21(lg2+lg5)+21lg2-2lg2
=21+19lg2
2.原式=lg5(lg5+lg2)+lg2
=lg5+lg2
=1