Answer:



Step-by-step explanation:
10.
The formula of a sum of terms of a geometric sequence:

We have:

Therefore:


Substitute a₁ = 5, r = 2 and n = 9:

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11.
We have

We know:

Therefore

Substitute:
![r^3=\dfrac{972}{-36}\\\\r^3=-27\to r=\sqrt[3]{-27}\\\\r=-3](https://tex.z-dn.net/?f=r%5E3%3D%5Cdfrac%7B972%7D%7B-36%7D%5C%5C%5C%5Cr%5E3%3D-27%5Cto%20r%3D%5Csqrt%5B3%5D%7B-27%7D%5C%5C%5C%5Cr%3D-3)
Calculate the first term:

Put a₁ = 12, r = -3 and n = 7 to the formula of a sum:

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12.
We have

We know:

Substitute:

Check for the given sum:
Substitute a₁ = 160, r = 1/2 and n = 6:

CORRECT :)