Find the sum of the geometric sequence –3, 15, –75, 375, … when there are 8 terms
1 answer:
First, we need to solve for the common ratio from the data given by using the equation.
a(n) = a(1) r^(n-1)
15 = -3 r^(2-1)
-5 = r
r = -5
Then, we can find the sum by the expression:
S(n) = a(1) ( 1 - r^n) / 1-r
S(8) = -3 (1 + 5^8) / 1+5
S(8) = -195313
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Answer:
![r = \sqrt[3]{\frac{3V}{4 \pi}}](https://tex.z-dn.net/?f=r%20%3D%20%5Csqrt%5B3%5D%7B%5Cfrac%7B3V%7D%7B4%20%5Cpi%7D%7D)
Step-by-step explanation:
From the formula of volume of a sphere we have to isolate "r" on one side of the equation i.e. we have to make "r" the subject of the equation.
![V=\frac{4}{3} \pi r^{3}\\\\ \text{Multiplying both sides by 3/4 we get}\\\\\frac{3V}{4} = \pi r^{3}\\\\ \text{Dividing both sides by } \pi \\\\ \frac{3V}{4 \pi} = r^{3}\\\\\text{Takeing cube root of both sides}\\\\\sqrt[3]{\frac{3V}{4 \pi}} = r](https://tex.z-dn.net/?f=V%3D%5Cfrac%7B4%7D%7B3%7D%20%5Cpi%20r%5E%7B3%7D%5C%5C%5C%5C%20%5Ctext%7BMultiplying%20both%20sides%20by%203%2F4%20we%20get%7D%5C%5C%5C%5C%5Cfrac%7B3V%7D%7B4%7D%20%3D%20%5Cpi%20r%5E%7B3%7D%5C%5C%5C%5C%20%5Ctext%7BDividing%20both%20sides%20by%20%7D%20%5Cpi%20%5C%5C%5C%5C%20%5Cfrac%7B3V%7D%7B4%20%5Cpi%7D%20%3D%20r%5E%7B3%7D%5C%5C%5C%5C%5Ctext%7BTakeing%20cube%20root%20of%20both%20sides%7D%5C%5C%5C%5C%5Csqrt%5B3%5D%7B%5Cfrac%7B3V%7D%7B4%20%5Cpi%7D%7D%20%3D%20r)
Therefore:
The denominator tells you the total amount of pieces.
