QUESTION :
FIND THE 18TH TERM OF THE ARITHMETIC SEQUENCE WHOSE 1ST TERM IS 11 AND WHOSE 7TH TERM IS 59.
(first we need to find the common difference (d)
Given a1 =11 , a7 =59 d ?
an = a1 + (n-1)d
59 =11 +(7-1)d
59=11 + (6) d
59-11 =(11-11) + 6d
48=6d
6d/6 = d
48/6 =8
d=8
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Other way to find the common difference (d)
d= An -A1 / n-1
Given : a1 =11 , a7 = 59 , d?
d=59-11 / 7-1
d= 48/6
d=8
NOW we have the (d) witch is the common difference
Given =A1 =11 ,An = 18 , d=8
An =A1 +(n-1)d
a¹⁸ =11 +(18-1)8
a¹⁸ = 11 +(17)8
a¹⁸= 11 + 136
a¹⁸ =147
THEREFORE THE 18TH TERM OF THE ARITHMETIC SEQUENCE is 147
