Cual es la formula de un octaedro
X^2 + y^2 = 8
X-y=0 so x = y
replace x = y into X^2 + y^2 = 8
y^2 + y^2 = 8
2y^2 = 8
y^2 = 8/2
y^2 = 4
y = - 2 and y = 2
because x = y
so x = - 2 and x = 2
solutions:
x= - 2 and x = + 2
y= - 2 and y = + 2
P = 4
13 + 3 = 16
16/4 = 4
These questions require reverse order, you have to work backwards
For example 4 * P you would do 4/P instead
well, if the diameter is 5, thus its radius must be half that, or 2.5, and therefore, the radius of the one four times as much will be (4)(2.5).
Let's simply get their difference, since that'd be how much more is needed from the smaller to larger sphere.
![~\hfill \stackrel{\textit{surface area of a sphere}}{SA=4\pi r^2}\qquad \qquad r=radius~\hfill \\\\[-0.35em] ~\dotfill\\\\ \stackrel{\textit{\large difference of their areas}}{\stackrel{\textit{radius of (4)(2.5)}}{4\pi (4)(2.5)^2}~~ - ~~\stackrel{\textit{radius of 2.5}}{4\pi (2.5)^2}}\implies 100\pi -25\pi \implies 75\pi ~~ \approx ~~235.62~ft^2](https://tex.z-dn.net/?f=~%5Chfill%20%5Cstackrel%7B%5Ctextit%7Bsurface%20area%20of%20a%20sphere%7D%7D%7BSA%3D4%5Cpi%20r%5E2%7D%5Cqquad%20%5Cqquad%20r%3Dradius~%5Chfill%20%5C%5C%5C%5C%5B-0.35em%5D%20~%5Cdotfill%5C%5C%5C%5C%20%5Cstackrel%7B%5Ctextit%7B%5Clarge%20difference%20of%20their%20areas%7D%7D%7B%5Cstackrel%7B%5Ctextit%7Bradius%20of%20%284%29%282.5%29%7D%7D%7B4%5Cpi%20%284%29%282.5%29%5E2%7D~~%20-%20~~%5Cstackrel%7B%5Ctextit%7Bradius%20of%202.5%7D%7D%7B4%5Cpi%20%282.5%29%5E2%7D%7D%5Cimplies%20100%5Cpi%20-25%5Cpi%20%5Cimplies%2075%5Cpi%20~~%20%5Capprox%20~~235.62~ft%5E2)
Hello from MrBillDoesMath!
Answer:
Choice E and F
Discussion:
From the quadratic formula with a = 3, b = -1, and c = 6
x = ( -b +\- sqrt(b^2 - 4ac) ) / (2a) => substitute in a,b,c from above
x = ( -(-1) +\- sqrt((-1)^2 - 4(3)(6)) / (2*3) => discriminant = 1 - 72 = -71)
x = ( 1 +\- sqrt(-71))/ 6
which are choices E and F
Thank you,
MrB
