I am stuck on what to do here.. The answer is +- 1/8 Q) Given that the first term of a geometric sequence is 4, and the third is 1, find possible values for the 6th term. Do you have to bring in logs or something? Thanks
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Originally Posted by Danielisew I am stuck on what to do here.. The answer is +- 1/8 Q) Given that the first term of a geometric sequence is 4, and the third is 1, find possible values for the 6th term. Do you have to bring in logs or something? Thanks $\displaystyle a_n=ar^{n-1}$ so $\displaystyle a_1=ar^{0} \iff 4=a$ now $\displaystyle a_3=4r^2 \iff \frac{1}{4}=r^2 \iff \pm \frac{1}{2}=r$ Finally we get $\displaystyle a_n=4(\pm \frac{1}{2})^{n-1}$ $\displaystyle a_6=4(\pm \frac{1}{2})^5= \pm \frac{1}{8}$
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