Find all ordered pairs (x, y) satisfying x + y = 12 and xy = 35.
Note
Here x and y are two numbers whose sum is 12 and product is 35. A useful HSC-level trick is to think of them as roots of the quadratic equation t² - (12)t + (35) = 0. After factoring or solving that quadratic, we get the two possible numbers. Since the question asks for ordered pairs, the order matters: if the two numbers are different, both (first, second) and (second, first) are valid. Checking the selected pair(s), each one has sum 12 and product 35. Therefore the correct answer choices are (5, 7), (7, 5).
