(lg2)^2 lg5×lg20-1

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

(lg2)^2 lg5×lg20-1
(lg2)^2 lg5×lg20-1

(lg2)^2 lg5×lg20-1
(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