Answer:
11) 195312
13) 5461
Step-by-step explanation:
11)
15÷(-3) = -5
(-75)÷15 = -5
375÷(-75) = -5
It’s clear that the common ratio of this geometric sequence is -5
Then using the sum formula for geometric sequences :
[tex]S_{11}=\left( -3\right) \times \frac{1-\left(-5 \right)^{8} }{1-(-5)} =-\frac{1}{2}\times(1-(-5)^8)=195312[/tex]
……………………………………………………
13)
[tex]S_{13}=1\times \frac{1-4^{7}}{1-4} =-\frac{1}{3} \times(1-4^{7})=5461[/tex]
