left =√AB *( 1/A+ 1/B)=√AB * 1/√A+√AB * 1/√B√B。

=√b/√a+√a/√b=√(b/a)+√(a/b), right =2.

Step 2-> Step 3, divide the left, move the 2 on the right to the left, and do it yourself.

Step 3-> Step 4, divide the molecules A and B into (√ a) 2, (√ b) 2,

The numerator on the left = (√ a) 2-2 √ a √ b+(√ b) 2 = (√ a-√ b) 2, and the denominator is √ab.