Datrys ar gyfer S_n
S_{n}=\frac{n\left(5n+9\right)}{2}
Datrys ar gyfer n
n=\frac{\sqrt{40S_{n}+81}-9}{10}
n=\frac{-\sqrt{40S_{n}+81}-9}{10}\text{, }S_{n}\geq -\frac{81}{40}
Rhannu
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S_{n}=\frac{n\left(5n+9\right)}{2}
Mynegwch \frac{n}{2}\left(5n+9\right) fel ffracsiwn unigol.
S_{n}=\frac{5n^{2}+9n}{2}
Defnyddio’r briodwedd ddosbarthu i luosi n â 5n+9.
S_{n}=\frac{5}{2}n^{2}+\frac{9}{2}n
Rhannu pob term 5n^{2}+9n â 2 i gael \frac{5}{2}n^{2}+\frac{9}{2}n.
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