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Find The Sum to each of the following: (Arithmetic Sequence)
1. Integer 1 to 50
2. Numbers between 1 and 81 are visible by 4.


Sagot :

Formula:
a_1)}{2} [/tex]
[tex]n= \frac{a_n-a_1}{d} +1[/tex]

1. There is obviously 50 terms here.
So: 
[tex]S_n= \frac{n(a_n+[tex]S_{50}= \frac{50(50+1)}{2} =25*51=1275[/tex]

2. The first term would be 4, and the last would be 80. The common difference is 4.
[tex]n= \frac{80-4}{4} +1= 20[/tex]
[tex]S_{20}= \frac{20(80+4)}{2} =840[/tex]