Kaplan CAT 4 question

Hi guys While reviewing a CAT exam by Kaplan I faced this question: What is the value of (x + y)2? (1) x2 − xy = 28 and 3xy + y2 = 72. (2) (x + y)4 = 10,000 Statement 1 is clearly enough to solve the issue, however in statement 2 kaplan explanation states that because (x + y)4 is the square of (x ...