(lg2)^2+lg5×lg20-1
=(lg2)^2+lg5×(lg2+lg10)-1
=(lg2)^2+lg5×(lg2+1)-1
=(lg2)^2+lg5×lg2+lg5-1
=lg2×(lg2+lg5)+lg5-1
=lg2×1+lg5-1
=lg2+lg5-1
=1-1
=0
(lg2)^2+lg5×lg20-1
=(lg2)^2+lg5×(lg2+lg10)-1
=(lg2)^2+lg5×(lg2+1)-1
=(lg2)^2+lg5×lg2+lg5-1
=lg2×(lg2+lg5)+lg5-1
=lg2×1+lg5-1
=lg2+lg5-1
=1-1
=0