[8.06] Which polynomial is a perfect square trinomial?
49x2 _ 28x + 16
4a2 _ 20a + 25
25b2 _ 20b _ 16
16x2 _ 24x _ 9
49x2 _ 28x + 16
4a2 _ 20a + 25
25b2 _ 20b _ 16
16x2 _ 24x _ 9