Like lg? 2
3.㏑ is the logarithm of ㏒ e basis, that is ㏒ ex = ㏑ x.
As long as you know that e≈2.7 in high school mathematics is often used to compare sizes, it can be eliminated even if you participate in the calculation, which is relatively simple.
1.lg5*lg20=lg﹙ 10÷2﹚×lg﹙ 10×2﹚=﹙lg 10-lg2﹚×﹙lg 10+lg2﹚=﹙ 1-lg2﹚×﹙ 1+lg2﹚= 1-lg? 2