Arithmetic sequences

[misty thorn]

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[safe ledge]

are these sums of arithmetic sequences or just arithmetic sequences @misty thorn

because if they are solely arithmetic sequences, you need to find the common difference

$d=a_{n+1}-a_{n}$ such that $a_n$ is the nth term in an arithmetic sequence

[raven crest]

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[safe ledge]

then you can use this formula to derive your arithmetic sequence

$a_n=a_1+(n-1)d$

[raven crest]

saddayyy_

[misty thorn]

they are sums

[safe ledge]

ok

so find the common difference

$S_2-S_1=d$

[raven crest]

saddayyy_

[safe ledge]

what is the common difference

@misty thorn

[misty thorn]

how would i write Sn in terms of n

[dusty hawk]

its something to do with the first term and the common difference

that’s your hint

[misty thorn]

?

[dusty hawk]

a_1 can be written as a+(1-1)d

[misty thorn]

So this formula

[dusty hawk]

oh

sun formula

oops

sorry

[dusty hawk]

okay first find what u_1 and d are

using what the other helper told you

[misty thorn]

u1 is 10 and d is 5

[dusty hawk]

nice, now just substitute them in and simplify

[vast thistle]

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[misty thorn]

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