Solution: x 2-y 2 is expanded by the square difference formula to get (x+y)(x-y), and then the common factor 2(x-y) is extracted and combined. In addition, ln refers to the natural logarithm, that is, the logarithm of X with E as the base, where E is a natural constant and an irrational number, which is approximately equal to 2.7 18288. For example, ln 1=loge 1=0, and the common logarithm is X pairs with 10 as the base-abbreviated as lg, for example, the logarithm with 10 as the base is recorded as LG 1 = 0.