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Help on question about sequences and series

Write down the term indicated in square brackets in each of the following arithmetic progressions

81, 77, 73, ... [nth term]


I did:
a=81, d=4
nth term = a+(n-1)d
81+(n-1)4 = 81+4n-4 = 73+4n


The answer is 85-4n


So somwhere I have gone wrong with the signs.
I'm not sure where though, as far as I can see i've done it all correct, evidentely not.
Your "nth term = ..." bit is wrong. Surely it's just nth term = a-nd?
Reply 2
Avatar for Pheylan
Pheylan
u1=81u_1 = 81

u2=77u_2 = 77

u3=73u_3 = 73

so un=81−4(n−1)u_n = 81 - 4(n - 1)
Reply 3
Avatar for elitespawn
elitespawn
d=-4 my dear!
Reply 4
Avatar for Kash:)
Kash:)
OP
15
elitespawn
d=-4 my dear!

Got it! Why didn't I see that before? :shy2: Thankyou

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