Arithmetic progression help please? Watch

razvimir
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Hi, Could you please help me on this question?

The nth term of an arithmetic progression is 6+5n. Find the sum of the first 20 terms.

How do i find a and d? then i use the sum to 20 terms formula yea?

thanks for your help in advance
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vc94
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substitute n=1,2,3 to find the first three terms and hence a and d.
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Gemini92
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(Original post by razvimir)
Hi, Could you please help me on this question?

The nth term of an arithmetic progression is 6+5n. Find the sum of the first 20 terms.

How do i find a and d? then i use the sum to 20 terms formula yea?

thanks for your help in advance
You know that the general nth term is a+(n-1)d. If you multiply out the brackets, you get a-d+dn=nth term. If you equate this to what you have above, you get 6+5n=a-d+dn. You can then work out a and d by equating the multiples of n and the constant term.
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razvimir
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omdz thats so simple! i was complicating it and overly thinking it. Thanks for your help
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