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Arithmetic Sequence question C2

Untfgditled.png

okay so i need help with the last part of the question:

i got -40 as A which is correct but i'm not sure how you find the first positive value?
____

I did Un > 0 therefore Un =-40 +(n-1)7

0 > 7n- 47
47 >7n
n =6.71 which is wrong as the answer is 2
Original post by Appazap
Untfgditled.png

okay so i need help with the last part of the question:

i got -40 as A which is correct but i'm not sure how you find the first positive value?
____

I did Un > 0 therefore Un =-40 +(n-1)7

0 > 7n- 47
47 >7n
n =6.71 which is wrong as the answer is 2


Aside from a minor slip.

Un>0 gives 7n>47, so n=7 is the smallest value.

The given answer of 2 is clearly wrong.

Edit: See below.
(edited 6 years ago)
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Appazap
OP
16
Original post by ghostwalker
Aside from a minor slip.

Un>0 gives 7n>47, so n=7 is the smallest value.

The given answer of 2 is clearly wrong.


Okay yeah that makes sense! Thank you.

The mark schemes working out was:

= −40 + 7k = −40 + 42 = 2

i don't know where they got K from
Original post by Appazap
Okay yeah that makes sense! Thank you.

The mark schemes working out was:

= −40 + 7k = −40 + 42 = 2

i don't know where they got K from


you aren't understanding the question... U got n as 7 which is correct and they question asked for the smaller positive term so now u know that the seventh term is the smallest positive term so and so now to find this the use the formula a+d (n-1) and they r saying that k = n-1....
hope you understand it now😊
Original post by Appazap
Okay yeah that makes sense! Thank you.

The mark schemes working out was:

= −40 + 7k = −40 + 42 = 2

i don't know where they got K from


well if u read the question carefully it says give the smallest positive term and not the position of the smallest term so the 7th term is the smallest positive term and no we have to find what what the 7th term is itself so they use the formula a+dk
where k = n-1
hope u understand it now:smile:
Reply 5
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Appazap
OP
16
Original post by brainmaster
well if u read the question carefully it says give the smallest positive term and not the position of the smallest term so the 7th term is the smallest positive term and no we have to find what what the 7th term is itself so they use the formula a+dk
where k = n-1
hope u understand it now:smile:


okay so what your saying is n=7

= -40+ (6x7)
=2


Ahhh you're correct. I understand now, i found n for which the smallest positive term occurs but i didn't find the actual term.


Thank you :smile:

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