Question

lg2+lg5=? 1-lg2=? 1-lg5=？ 2lg5+2/3lg8+lg5*lg20+(lg2)2=?

Answer 1

lg2+lg5=lg2*5=lg10=1
1-lg2=lg10-lg2=lg(10/2)=lg5
2lg5+2/3lg8+lg5*lg20+(lg2)^2=2lg(10/2)+2/3lg(2^3)+lg(10/2)*lg(10*2)+(lg2)^2
=2-2lg2+2lg2+(1-lg2)(1+lg2)+(lg2)^2
=2+1-(lg2)^2+(lg2)^2
=3

Answer 2

lg2+lg5=lg10=1
1-lg2=lg5
1-lg5=lg2
2lg5+2/3lg8+lg5*lg20+(lg2)2
=2lg5+2lg2+lg5*(1+lg2)+(lg2)^2
=2+lg5+lg5*lg2+(lg2)^2
=2+lg5+lg2*(lg5+lg2)
=2+lg5+lg2
=3