Найдите s5, если a1=64 q=1/4

[latex]S_n= \dfrac{a_1\cdot(1-q^n)}{1-q} \\ \\ \\ S_5= \dfrac{a_1\cdot(1-q^5)}{1-q} = \dfrac{64\cdot(4^5-1)}{4^5-4^4} = \dfrac{4^3(4^5-1)}{4^3(4^2-4)} = \dfrac{4^5-1}{4^2-4} =85.25[/latex]