(a) The given terms 4,9,16,25 are perfect squares (eg: 16 = 4^2 and 5^2 = 25). The next set of perfect squares are 6^2 = 36, 7^2 = 49 and 8^2 = 64.
(b) Similar to the previous part. This time the next three terms are 25, 36, and 49 because 5^2 = 25, 6^2 = 36 and 7^2 = 49.
(c) We start at 1 and add 3 each time. This sequence is arithmetic. The next term after 10 is 10+3 = 13. After that is 13+3 = 16. Finally 16+3 = 19 is the last term we need.
(d) Similar to part (c) earlier. This time we start at 3 and add 6 each time. The next three terms are 21+6 = 27, and 27+6 = 33, and finally 33+6 = 39
Answer: the addition of xy would make it a polynomial because it cannot simplify and the equation would have 3 different set of numbers that could not combine.