lg5^2+2lg2-lg2^2
=2lg5+2lg2-2lg2
=2lg5;

(lg5)^2+2lg2-(lg2)^2?
=(lg5)^2-(lg2)^2+2lg2
=(lg5+lg2)(lg5-lg2)+lg2²
=lg10*lg5/2+lg4
=1*lg5/2+lg4
=lg[(5/2)*4]
=lg10
=1