9514 1404 393
Answer:
Step-by-step explanation:
First differences are ...
x -4, 8 -x, y -8, 20 -y
Then second differences are ...
(8 -x) -(x -4)
(y -8) -(8 -x)
(20 -y) -(y -8)
Each of these is said to be 2, so we have ...
12 -2x = 2 ⇒ x = 5
28 -2y = 2 ⇒ y = 13
And an equation we can use to check:
x +y -16 = 2 ⇒ 5 +13 -16 = 2 . . . . true
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The explicit formula for the sequence is ...
an = n^2 -2n +5
