Question

Pls help and explain tyyy

Answer 1

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 :

$S_{11}=\left( -3\right) \times \frac{1-\left(-5 \right)^{8} }{1-(-5)} =-\frac{1}{2}\times(1-(-5)^8)=195312$

……………………………………………………

13)

$S_{13}=1\times \frac{1-4^{7}}{1-4} =-\frac{1}{3} \times(1-4^{7})=5461$