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If as = 24, a, = 40, then find a20

If as = 24, a, = 40, then find a20-example-1

1 Answer

8 votes

Answer:


a_(20) = 84

Explanation:


a_(n) =
a_(1) + ( n - 1 )d

~~~~~~~~~~~~~


a_(5) =
a_(1) + (5 - 1)d = 24


a_(9) =
a_(1) + (9 - 1)d = 40


a_(1) + 4d = 24 ........... (1)


a_(1) + 8d = 40 ........... (2)

(2) - (1)

4d = 16 ⇒ d = 4


a_(1) + 8(4) = 40 ⇒
a_(1) = 8


a_(20) = 8 + ( 20 - 1 ) × 4 = 84

User Stephen Pellicer
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