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19
You need 12 terms to get a sum of 636 in the arithmetic progression.
1. This is the arithmetic progression:
9 17 25 33 ...
+8 +8 +8 +8
2. There is a rule to get de last term of the progression:
where:
Is the last term
Is de first term
Is the amount of terms
Is the difference between terms
We replace the values:
...(1)
3. The rule to get the SUM is:
.. (2)
We can replace (1) in (2)
This kind of equation have this rule:
Replacing values:
We have two options:
We take the value n=12
vivipaoto23:
muy bien
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