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Sagot :
Answer:
[tex]\sum_{n = 1}^{7} -2 -2n[/tex]
Step-by-step explanation:
Arithmetic sequence:
In an arithmetic sequence, the difference of consecutive terms is always the same, called common difference.
The nth term of a sequence is given by:
[tex]a_{n} = a_1 + (n-1)d[/tex]
In which [tex]a_1[/tex] is the first term and d is the common difference.
Sigma notation to represent the sum of the first seven terms
Sum going from the index starting at 1 and finishing at 7, that is:
[tex]\sum_{n = 1}^{7} f(n)[/tex]
Now we have to fund the function, which is given by an arithmetic sequence.
−4, −6, −8,
First term -4, common difference - 6 - (-4) = -6 + 4 = -2, so [tex]a_1 = -4, d = -2[/tex]
Then
[tex]f(n) = a_{n} = a_1 + (n-1)d[/tex]
[tex]f(n) = -4 + (n-1)(-2)[/tex]
[tex]f(n) = -4 - 2n + 2 = -2 - 2n[/tex]
Sigma notation:
Replacing f(n)
[tex]\sum_{n = 1}^{7} -2 -2n[/tex]
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