What is the value of y in the arithmetic sequence y + 6, 12, 3y?
y + 6 + d = 12
so d = 6-y
12 + d = 3y
d = 3y-12
equate the d's (red equations)
6-y = 3y-12
4y = 18
y = 4.5
Just to add that "d" in the above stands for the difference between terms in the arithmetic sequence.
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