Question

СРОЧНО!!!ДОПОМОЖІТЬ БУДЬ ЛАСКА
b1=15 q=1/3 S5?

Answer 1

$\displaystyle\bf\\b_{1} =15\\\\q=\frac{1}{3} \\\\S_{5} =?\\\\\\S_{5} =\frac{b_{1} \cdot(1-q^{5}) }{1-q} =\frac{15\cdot\Big[1-\Big(\dfrac{1}{3} \Big)^{5} \Big]}{1-\dfrac{1}{3} } =\frac{15\cdot\Big(1-\dfrac{1}{243}\Big) }{\dfrac{2}{3} } =\\\\\\=\frac{15\cdot\dfrac{242}{243} }{\dfrac{2}{3} } =\frac{15\cdot 242\cdot 3}{243\cdot 2} =22\frac{11}{27}$