Answer:
Step-by-step explanation:
Formula
Sn = (a + a + (n - 1)*d) * n / 2
Givens
Sn = 60
a = 3
Solution
You want integer values for d and n
60 = (2*a + (n - 1)*d) * n/2 Multiply both sides by 2
120 = (2*3 + (n - 1)*d ) * n
120 = (6 + n*d - d) * n
120 = 6n + n^2*d - d*n
This gives some really wild results. I will list all of them here. and then discuss them.
These are the ones that give results without any question and are correct.
n d tn
2 54 3 57
3 17 3 20 37
4 8 3 11 19 27
Here are some that are the gift of the equation
20 0 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
Now the equation says the following 3 are correct, but are they? Can you have a negative n? The equation says yes, but I doubt your instructor will.
-5 5
-1 63
-2 22
You can bring these up if you are in a classroom. I wouldn't if you have to submit this to a computer which has absolutely no ability whatever to think about exceptions. Even the 20 0 is one I wouldn't use.
