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In a geometric sequence, the 1st term is 8 and the 3rd term is 72. Given a positive common ratio, find the 7th term.

Sagot :

Answer:

see explanation

Step-by-step explanation:

The n th term of a geometric sequence is

= a

where a is the first term and r the common ratio

Both a and r have to be found

Given a₃ = - 2, then

ar² = - 2 → (1)

Given a₇ = - 32, then

a = - 32 → (2)

Divide (2) by (1)

= , that is

= 16 ( take the fourth root of both sides )

r = 2 ← common ratio

Substitute r = 2 into (1)

a × 2² = - 2, that is

4a = - 2 ( divide both sides by 4 )

a = -  ← first term

Hence

= -  ← explicit formula

and

= -  ×  = - 0.5 × 512 = - 256

Step-by-step explanation:

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