Answer: Choice A
a_n = 7 + (n-1)*(-4)
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Step-by-step explanation:
The given set of equations tell you two things
* The first term is 7 because a_1 = 7. When I write "a_1", I mean "a subscript 1" where the 1 is smaller and to the right and slightly below 'a'. This will apply with a_n and a_(n-1) as well.
* The nth term a_n is found by subtracting 4 from the previous term a_(n-1). So the common difference is d = -4
So,
a_n = a_1 + d*(n-1)
a_n = 7 + (-4)*(n-1)
a_n = 7 + (n-1)*(-4)
which is choice A