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I have tried by using the formula

$$a_n=a+(n-1)d$$

And answer is coming -3

I have done it like in this way

$$a_n = a+(n-1)d$$ $$4=a+(4-1)×(-4)$$ $$a=-12/4$$ $$a= -3$$

Bernard
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Chirag Agrawal
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  • include more working please. you don't want to cause multiple people to repeat your work. – Siong Thye Goh Mar 29 '18 at 05:29
  • I couldn't understand what r u trying to tell – Chirag Agrawal Mar 29 '18 at 05:36
  • He is trying to ask you to show your calculations. What did you use for $n$? What did you use for $d$? Where did the number $-3$ come from? There are certainly things wrong with your calculations and we could tell you the correct answer, but it would be much more helpful for you if you see why what you already tried yourself was incorrect and why and how to fix it. – JMoravitz Mar 29 '18 at 05:38
  • As an aside, even if you weren't going to use short-cut formulae to get to the answer, you should be able to brute-force it to check since the numbers are so small. If the seventh term is $4$, then what is the sixth term? Given the sixth term, what is the fifth, and so on... you should be able to see very quickly that $-3$ is way off. – JMoravitz Mar 29 '18 at 05:40
  • Pleas tell me full calculation by solving it – Chirag Agrawal Mar 29 '18 at 05:42
  • Now that we see some of your work, lets analyze it. Here, $n$ refers to which term it is. We are talking about the seventh term, so we use $7$ in place of $n$. So, we should have had $A_7=a+(7-1)\times(-4)$. Next, we want to isolate $a$ by itself. To do that, let us first subtract $(7-1)\times(-4)$ from each side... You divided for whatever reason thinking that that would do something useful. – JMoravitz Mar 29 '18 at 05:45
  • not trying to make your life difficult, try to include as much details as possible as first we won't have to repeat your work, we get to see your work and point out your mistake. Also posts without attempt tend to get negative votes and closure votes, welcome to MSE. note that you might not get full solution each time, I tend to give hints sometimes as sometimes I believe it helps others learn better. Also useful link to type maths on this site: mathjax – Siong Thye Goh Mar 29 '18 at 05:50

1 Answers1

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$$a_7 = a+(7-1)d$$ $$4=a+(7-1)×(-4)$$ $$4 = a-24$$ $$4+24 = a$$

Your mistakes:

  • The right $n$ should be $7$.

  • Ignoring previous mistake, for some reason, you just go from $4=a-12$ to $a=-12/4$. The right action should have been add $12$ to both sides.

Siong Thye Goh
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