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# Help 4 ​

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Help 4 Mar 8, 2018

#1
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4) The sequence is certainly arithmetic! Notice that $${\underbrace{13,}\underbrace{20,}\underbrace{27,}34,...}\\ +7+7+7$$ . In other words, the common difference is 7.

5) This is another arithmetic sequence with a common difference of -7.

Remember that awesome formula that tells you the nth term of an arithmetic sequence? It's $$a_n=a_1+d(n-1)$$ . Let's use it!

$$a_n=a_1+d(n-1)\\ a_{50}=5-7(50-1)\\ a_{50}=5-7*49\\ a_{50}=-338$$

6) The arithmetic mean is also the average.

$$a_n=\frac{a_{n-1}+a_{n+1}}{2}\\ a_n=\frac{3.9+7.1}{2}\\ a_n=\frac{11}{2}\\ a_n=5.5$$

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Mar 8, 2018

#1
+1

4) The sequence is certainly arithmetic! Notice that $${\underbrace{13,}\underbrace{20,}\underbrace{27,}34,...}\\ +7+7+7$$ . In other words, the common difference is 7.

5) This is another arithmetic sequence with a common difference of -7.

Remember that awesome formula that tells you the nth term of an arithmetic sequence? It's $$a_n=a_1+d(n-1)$$ . Let's use it!

$$a_n=a_1+d(n-1)\\ a_{50}=5-7(50-1)\\ a_{50}=5-7*49\\ a_{50}=-338$$

6) The arithmetic mean is also the average.

$$a_n=\frac{a_{n-1}+a_{n+1}}{2}\\ a_n=\frac{3.9+7.1}{2}\\ a_n=\frac{11}{2}\\ a_n=5.5$$

TheXSquaredFactor Mar 8, 2018