a. As you can see, the sequence starts at -3, and increases by 7 each time, Amanda is wrong because she found the following formula:
an = 18 + 7(n - 1)
For n =1 the result should be -3:
n = 1
a1 = 18 + 7(1 - 1) = 18 + 7(0) = 18 + 0 = 18, she miscalculated the first term, and the whole sequence in general.
b. A possible sequence identification could be:
an = 7n - 10
Let's verify it:
n=1
a1 = 7(1) - 10 = 7 - 10 = -3
n=2
a2 = 7(2) - 10 = 14 - 10 = 4
n=3
a3 = 7(3) - 10 = 21 - 10 = 11
and so on...
Now for n=58
a58 = 7(58) - 10 = 396
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32 = 2 + 3(n - 1)
Solving for n:
Use distributive property on the right hand side:
32 = 2 + 3n - 3
32 = 3n - 1
Add 1 to both sides:
32 +1 = 3n - 1 + 1
33 = 3n
Divide both sides by 3:
33/3 = 3n/3
11 = n
n = 11
