[질문] 등차수열의합공식과등비수열의합공식은??

등차:첫째항a,공차d,인등차수열의n항까지의합Sn=n{2a+(n-1)d}/2 등비:첫째항a,공비r,등비수열의n항까지의합Sn=a(1-r^n)/(1-r)공비가1일때는a곱하기r