The expression y=15x-20 is not a formula for the nth term of the sequence.
An ordered list of elements following a certain formula by which the next term can be determined are said to be in sequence.
Given that, A sequence is represented below,
-20, -5, 10, 25, 40
The sequence is increasing by 15, therefore it is an arithmetic sequence
The first term (a) is -20
Common difference (d) = -20-(-5) = 20+5 = 15
The nth term of an arithmetic sequence is given by,
aₙ = a+(n-1)ₓd
Where aₙ is the nth term, d is common difference, a is the first term.
Here, a = -20, d = 15
Therefore, nth term is
aₙ = -20+(n-1)15
If we write it in the form of a function, then,
f(x) = -20+15(n-1)
In slope intercept form,
y = 15x-35
Hence, the only expression that can not define the nth term of the sequence is y = 15x-20
For more references on the sequences, click;
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