Use the formula for the general term (the nth term) of a geometri...

Question

Use the formula for the general term (the nth term) of a geometric sequence to find the indicated term of the sequence. Find a(sub 5) when a(sub 1) = -3, r = 2

Accepted Answer

Welcome back. I'm so glad you're here. We've got a geometric sequence with some givens. We know that a sub one or the value of the first term in the sequence is negative seven. We know that our our the ratio equals two and we want to find the value of a sub eight or the eighth term in our sequence because it's a sub eight. We know that that's going to be the end term we're looking for or N equals eight. And we know from previous lessons that we have a formula for that A sub N equals a sub one of the value of the first term times Are the ratio raised to the N. The number minus one. And we know all these things. We can fill them right in. So a sub one that's negative seven times are is two raised to the N, which is 8 -1. Now we can simplify that. We've got negative seven times to race to the seventh. Well that's negative seven times 128 to race to the seventh is 128 and negative seven times 128 is negative 896. That leaves us with answer choice B. Well done. We'll catch on the next one

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Use the formula for the general term (the nth term) of a geometric sequence to find the indicated term of the sequence. Find a(sub 5) when a(sub 1) = -3, r = 2