Question

Допоможіть будь ласочка з алгеброю даю 100 балів ​

Answer 1

$\displaystyle\bf\\3)\\\\b_{1} =28\\\\b_{2} =-14\\\\\\b_{2} =b_{1} \cdot q\\\\q=b_{2} :b_{1}=-14:28=-0,5 \\\\\\S=\frac{b_{1} }{1-q} =\frac{28}{1-(-0,5)}=\frac{28}{1+0,5} =\frac{28}{1,5} = 18\frac{2}{3} \\\\\\Otvet \ : \ S=18\frac{2}{3} \\\\4)\\\\a_{1} =10,3\\\\d=-0,5\\\\a_{n} =7,3\\\\\\a_{n} =a_{1} +d\cdot(n-1)\\\\7,3=10,3-0,5\cdot(n-1)\\\\0,5\cdot(n-1)=3\\\\n-1=6\\\\n=7\\\\Otvet \ : \ a_{7} =7,3$