SOLUTION: Find the indicated sum: 6 + 12 + 18 + ... + 300

One of two formula for the sum of n terms is



We have a1 = 6 and an = 300

so we must find d and n

6 + 12 + 18 + ... + 300

First we determine the common difference, d

d = (2nd term)-(1st term) = (3rd term)-(2nd term) = 12-6 = 18-12 = 6

Next we determine the number of terms, n:

We use the formula for the nth term













Now we can substitute in









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Notice that we could have used the other sum formula just as well:













Edwin