If
is the first number in the progression, and
is the common ratio between consecutive terms, then the first four terms in the progression are
![\{x,xr,xr^2,xr^3\}](https://tex.z-dn.net/?f=%5C%7Bx%2Cxr%2Cxr%5E2%2Cxr%5E3%5C%7D)
We want to have
![\begin{cases}xr^2-x=12\\xr^3-xr=36\end{cases}](https://tex.z-dn.net/?f=%5Cbegin%7Bcases%7Dxr%5E2-x%3D12%5C%5Cxr%5E3-xr%3D36%5Cend%7Bcases%7D)
In the second equation, we have
![xr^3-xr=xr(r^2-1)=36](https://tex.z-dn.net/?f=xr%5E3-xr%3Dxr%28r%5E2-1%29%3D36)
and in the first, we have
![xr^2-x=x(r^2-1)=12](https://tex.z-dn.net/?f=xr%5E2-x%3Dx%28r%5E2-1%29%3D12)
Substituting this into the second equation, we find
![xr(r^2-1)=12r=36\implies r=3](https://tex.z-dn.net/?f=xr%28r%5E2-1%29%3D12r%3D36%5Cimplies%20r%3D3)
So now we have
![\begin{cases}9x-x=12\\27x-3x=36\end{cases}\implies x=\dfrac32](https://tex.z-dn.net/?f=%5Cbegin%7Bcases%7D9x-x%3D12%5C%5C27x-3x%3D36%5Cend%7Bcases%7D%5Cimplies%20x%3D%5Cdfrac32)
Then the four numbers are
![\left\{\dfrac32,\dfrac92,\dfrac{27}2,\dfrac{81}2\right\}](https://tex.z-dn.net/?f=%5Cleft%5C%7B%5Cdfrac32%2C%5Cdfrac92%2C%5Cdfrac%7B27%7D2%2C%5Cdfrac%7B81%7D2%5Cright%5C%7D)
Step-by-step explanation:
First, the pizza is 18 inches in diameter, so
![d = 18](https://tex.z-dn.net/?f=d%20%3D%2018)
and, because the radium is half of the diameter,
![r = 9](https://tex.z-dn.net/?f=r%20%3D%209)
<u>Note that the units are inches.</u>
Using the equation
![a = \pi r ^{2}](https://tex.z-dn.net/?f=a%20%3D%20%5Cpi%20%20r%20%5E%7B2%7D%20)
where a is the area of a circle, we know that the area of the whole pizza is approx.254.5 square inches. Divide by 8 to find the area of 1/8 of a pizza. Each slice will have an area of approx. 32 square inches. For a precise result, the answer is
![a(s)= \frac{(\pi \times 9^{2})}{s}](https://tex.z-dn.net/?f=a%28s%29%3D%20%20%5Cfrac%7B%28%5Cpi%20%20%5Ctimes%209%5E%7B2%7D%29%7D%7Bs%7D%20)
where a(s) is the area of a slice of pizza, and s is the total number of slices, given they are equal in size.