Answers

2016-07-07T22:44:51+08:00
The answer of your problem is -11/5
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  • Brainly User
2016-07-08T02:58:25+08:00
Note:  Here, I solve the sum of the arithmetic series using the complete formula.

 S_{n}= \frac{n}{2}  [2(a₁) + (n-1)(d)]

n = 12      a₁= 1/5       d =-1/2

S₁₂ = 12/2 [2(1/5) + (12-1)(-1/2)]

S₁₂ = 6 [2/5 + (11)(-1/2)]

S₁₂ = 6 [2/5 - 11/2]

S₁₂ = 6 [ \frac{4-55}{10}

S₁₂ = 6 (-11/10)

S₁₂ = 3 (-11/5)

S₁₂ = -33/5  
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