Suatu barisan aritmatika suku ke -2 dan suku ke-5 masing-masing 19 dan 31. jumlah suku 30 pertama adalah..
a. 2280
b.2190
c.1815
d.364
tolong bantu pake cara
a. 2280
b.2190
c.1815
d.364
tolong bantu pake cara
IcukSugiarto
![sehingga\ untuk\ jumlah\ 30\ suku\ pertama:\\\boxed{S_{n}= \frac{n}{2} (2a+ (n-1)b)}\\\boxed{S_{30}= \frac{30}{2} (2(15)+ (30-1)4)}\\\boxed{S_{30}= 15 (30+ (29)4)}\\\boxed{S_{30}= 15 (30+ 116)}\\\boxed{S_{30}= 15 (146)}\\\boxed{S_{30}= 2190}~~~~~~\Rightarrow~~[Solved]~~~~~\bold{[b.~~2190]}](https://tex.z-dn.net/?f=sehingga%5C+untuk%5C+jumlah%5C+30%5C+suku%5C+pertama%3A%5C%5C%5Cboxed%7BS_%7Bn%7D%3D++%5Cfrac%7Bn%7D%7B2%7D+%282a%2B+%28n-1%29b%29%7D%5C%5C%5Cboxed%7BS_%7B30%7D%3D++%5Cfrac%7B30%7D%7B2%7D+%282%2815%29%2B+%2830-1%294%29%7D%5C%5C%5Cboxed%7BS_%7B30%7D%3D++15+%2830%2B+%2829%294%29%7D%5C%5C%5Cboxed%7BS_%7B30%7D%3D++15+%2830%2B+116%29%7D%5C%5C%5Cboxed%7BS_%7B30%7D%3D++15+%28146%29%7D%5C%5C%5Cboxed%7BS_%7B30%7D%3D++2190%7D%7E%7E%7E%7E%7E%7E%5CRightarrow%7E%7E%5BSolved%5D%7E%7E%7E%7E%7E%5Cbold%7B%5Bb.%7E%7E2190%5D%7D "sehingga\ untuk\ jumlah\ 30\ suku\ pertama:\\\boxed{S_{n}= \frac{n}{2} (2a+ (n-1)b)}\\\boxed{S_{30}= \frac{30}{2} (2(15)+ (30-1)4)}\\\boxed{S_{30}= 15 (30+ (29)4)}\\\boxed{S_{30}= 15 (30+ 116)}\\\boxed{S_{30}= 15 (146)}\\\boxed{S_{30}= 2190}~~~~~~\Rightarrow~~[Solved]~~~~~\bold{[b.~~2190]}")
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