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3 years ago

The 70th term of an arithmatic sequence is 121.5 the common difference is 1.5. Find a12. (write a rule to find a12)

Mathematics

2 answers:

Katen [24]3 years ago

8 0

Answer:

$a_{12}$ = 34.5

Step-by-step explanation:

The n th term of an arithmetic sequence is

$a_{n}$ = a₁ + (n - 1)d

where a₁ is the first term and d the common difference

Given $a_{70}$ = 121.5, then

a₁ + (69 × 1.5) = 121.5

a₁ + 103.5 = 121.5 ( subtract 103.5 from both sides )

a₁ = 18

Hence

$a_{12}$ = 18 + (11 × 1.5) = 18 + 16.5 = 34.5

yaroslaw [1]3 years ago

5 0

Answer:

12th term = 34.5

Step-by-step explanation:

l = a + (n-1)*d

d = 1.5

70th term = 121.5

a + 69 * 1.5 = 121.5

a + 103.5 = 121.5

a = 121.5 - 103.5

a = 18

12 th term = 18 + 11 * 1.5 = 18 + 16.5 = 34.5

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