Quadratic sequences
If the difference between the terms changes, this is called a quadratic sequence. If you use the formula n 2 + n to make a sequence, it means that: When n = 1 you get = 2When n = 2 you get = 6When n = 3 you get = 12When n = 4 you get = 20- giving the sequence 2, 6, 12, 20.
Here, the differences between terms are not constant, but there is still a pattern.- the first differences increase by 2 each time- the second increases by 2
Learn these rules:If the second difference is 2, you start with n 2.If the second difference is 4, you start with 2n 2.If the second difference is 6, you start with 3n 2.