Question 1164214
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The tutor @greenestamps has a great way to see why your teacher has most likely made a typo/mistake of some kind. Here's another clue that the problem is faulty. 


"the first three terms of the new sequence are 3, 7, and 11" means the new sequence is arithmetic. Each time we're adding 4 to get the next term. This is of course assuming the pattern holds up.


But adding a GP and AP together does not lead to an arithmetic sequence unless the common ratio of the GP is r = 0 or r = 1.


Consider the sequence {0,0,0,0,...} which is geometric with r = 0. Adding this to any AP leads to the same AP. This isn't too exciting, but it's still important to know. If r = 1, then something like {4,4,4,...} is geometric which means we shift all of the terms of an AP by 4, meaning the new sequence is also an AP as well.


But for r = 2 and larger is when the sum is no longer arithmetic. 
Something like {1,2,4,8,...} will add onto an AP to make some non-arithmetic sequence. This is because the gap from 1 to 2 is smaller than the gap from 2 to 4, and the gap widens each time. There's no way to have a fixed width the entire time. This will reflect in the new sequence as well. 


I would ask your teacher for clarification.
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