#### Puly Mohloai

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- Thread starter Puly Mohloai
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I wonder if you copied something incorrectly, since [imath]kn^2+3n^2[/imath] seems unlikely.

Please show us an image of the actual problem. Also, tell us what you have learned about the sum of an arithmetic series, so we can start with that.

- Joined
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@ Dr P No, I think it is correct. It does work out.I wonder if you copied something incorrectly, since [imath]kn^2+3n^2[/imath] seems unlikely.

Please show us an image of the actual problem. Also, tell us what you have learned about the sum of an arithmetic series, so we can start with that.

@ Puly

Have you found \(\displaystyle S_1\)? Do you realise that this will be equal to the first term \(\displaystyle t_1\)?

Have you found \(\displaystyle S_2\)? What will \(\displaystyle S_2 - S_1 \) give you?

Can you continue until you have the first 5 terms of the arithmetic sequence?