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Answer:
S₁₂ = - 654
Step-by-step explanation:
there is a common difference between consecutive terms , that is
- 14 - (- 5) = - 23 - (- 14) = - 32 - (- 23) = - 9
this indicates the series is arithmetic with sum to n terms
=
[ 2a₁ + (n - 1)d ]
where a₁ is the first term and d the common difference
here a₁ = - 5 and d = - 9 , then
S₁₂ = [ (2 × - 5) + (11 × - 9) ]
= 6(- 10 - 99 )
= 6 × - 109
= - 654