Oblicz pierwszy wyraz ciągu jeśli:
a)q=2 S4=60
S_n=\frac{a_1(1-q^n)}{1-q}
\frac{a_1(1-2^4)}{1-2}=60
a_1*(1-16)=60*(-1)
a_1=\frac{-60}{-15}=4
b)q=1/2 S4=2046
\frac{a_1(1-(\frac{1}{2})^4)}{1-\frac{1}{2}}=2046
\frac{a_1(1-\frac{1}{16} )}{\frac{1}{2}}=2046
a_1\frac{15}{16}*2=2046
a_1=2046*\frac{8}{15}=1091\frac{3}{15}