Bea L.

asked • 08/17/17

in an arithmetic sequence the 3rd term is 16 the 7th is 34 find the 1st term common difference and 12th term

Please answer as soon as possible!😞 This is for my friend and not for me 😅 Its her exam tomorrow 😕 Thank you do much in advance!😁💓

1 Expert Answer

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Andrew M. answered • 08/17/17

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a3 = 16
a7 = 34
 
a7 = a3 + 4d    where d is the common difference
34 = 16 + 4d
18 = 4d
d = 18/4 = 4.5
 
a1 = a3 - 2d = 16 - 2(4.5) = 16-9 = 7
 
a12 = a1 + 11d = 7 + 11(4.5) = 56.5
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Andrew M.

You can also check for a12 with the following:
 
a12 = a3 + 9d = 16 + 9(4.5) = 56.5
 
a12 = a7 + 5d = 34 + 5(4.5) = 56.5
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08/17/17

Bea L.

OMGG THANKK YOUU SO MUCH ??
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08/17/17

Andrew M.

You're very welcome.
I wish your friend luck on her exam.
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08/17/17

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