In the top left-hand cage, we need to divide two numbers to produce a sum of 2 (Fig #4). Numerically, the two possibilities are 2 divided by 1 or 4 divided by 2. However, KenKen requires every number to appear in every row and column without repeating, so row one, column two must contain a 4 and eureka! row one, column one must contain a 2.
Complete A Column