The 8th term of a linear sequence is 18 and the 12th term is 26.find the first. The common difference the 20th term

Answer 1

In this sequence:

a8 = a1 + 7 d = 18 , a12 = a1 + 11 d = 26

Now solve system:

a1 + 7 d = 18

a1 + 11 d = 26

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a1 + 7 d = 18
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a1 + 11 d = 26
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a1 - a1 + 7 d - 11 d = 18 - 26

0 - 4 d = - 8

- 4 d = - 8

d = - 8 / - 4 = 2

a1 + 7 d = 18

a1 + 7 ∙ 2 = 18

a1 + 14 = 18

a1 = 18 - 14 = 4

a20 = a1 + 19 d = 4 + 19 ∙ 2 = 4 + 38 = 42

Answer 2

Please 8th by 26 term