# Math

Given that T7=23,Tn=43 and T2n=91.for an A.P.find a,d and n...help please

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1. T7=a+6d=23
Tn=a+[n-1]d=43
T2n=a+[2n-1]=91
subtract equ 2 from equ 3 give
nd=48---equ 4
from equ2 nd=43+d-a
:- 48=43+d-a
5=d-a ---equ6 recall from equ1 a=23-6d put the value of a into equ 6
d=4 from equ4 nd=48 since d=4, n=12
put the value of d into equ1 :- a=-1
(n=12,d=4,a=-1]

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posted by joshua
2. Thank you

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posted by favour

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