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maths help

we've not covered this yet, but could anyone explain how you would work out


the tenth term of an arithmetic progression is 125 and the sum of the first ten terms is 260. show that the first term in the progression is -73

is there a formula or a simple way to work this out?
Reply 1
Avatar for Alexb01
Alexb01
From formula book:

Un = a + (n-1)d (nth term)
Sn = n/2[2a+(n-1)d] (sum of the first n terms)

So from the information you've been given:

u10 = 125 = a + 9d
S10 = 260 = 5(2a + 9d)

And so you have 2 simultaneous equation to solve...

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