150K Before WOA 2010

[xforeverxmetalx]

it seemed to be correct

about the things you didn't calculate, see next post

Ah, good thing The one with the chemical spill at least is probably wrong... saw a question on the final where they didn't give you the starting values. But I probably got that one right then because it was multiple choice and I could check.

 

[Nidan]

WARNING: This post contains a high amount of math

might be a bit late now but

That's assuming 130's the starting point... because otherwise I don't know. Most problems tell you where it starts, rather than at the 4hr and 12hr mark...

the starting point is easy to calculate
according to the formula you used above you get
130 = start * 0,955^4 => start =156.290

That's assuming 130's the starting point... because otherwise I don't know. Most problems tell you where it starts, rather than at the 4hr and 12hr mark...

you math looks correct, about the starting point see above

x = length of each side of the square needed to be cut out

long size = 20-2x
short size = 15-2x

volume of rectangle = L x W x H = (20-2x)(15-2x)x

Then you stick that in graphing calculator, makes something that looks either like /\/ or \/\... find the peak [one not going to infinity and beyond] and that's the max volume.

Which I'm not going to find atm, because my calculator is currently in the car.

who needs a graphic calculator...
we have (20 - 2x)(15 - 2x)x = 300x - 70x^2 + 4x^3 =: f(x)
so f'(x) = 300 - 140x + 12x^2
now we need to solve f'(x) = 0
x = 70 +/- sqrt(70^2 - 300) = 70 +/- 67,823 = 2,176 or 137,823
now checking which one is the maximum using f''(x)
f''(x) = -140 + 24x => f''(2,176) = -87,759 < 0 ; f''(127,823) = 3167,759 > 0
so for x=2,176 we have a (local) maximum (and for x=137,823 a minimum which is not what we want)

 

[Nidan]

Ah, good thing The one with the chemical spill at least is probably wrong... saw a question on the final where they didn't give you the starting values. But I probably got that one right then because it was multiple choice and I could check.

well, whatever works

 

[xforeverxmetalx]

WARNING: This post contains a high amount of math

might be a bit late now but

the starting point is easy to calculate
according to the formula you used above you get
130 = start * 0,955^4 => start =156.290

you math looks correct, about the starting point see above

who needs a graphic calculator...
we have (20 - 2x)(15 - 2x)x = 300x - 70x^2 + 4x^3 =: f(x)
so f'(x) = 300 - 140x + 12x^2
now we need to solve f'(x) = 0
x = 70 +/- sqrt(70^2 - 300) = 70 +/- 67,823 = 2,176 or 137,823
now checking which one is the maximum using f''(x)
f''(x) = -140 + 24x => f''(2,176) = -87,759 < 0 ; f''(127,823) = 3167,759 > 0
so for x=2,176 we have a (local) maximum (and for x=137,823 a minimum which is not what we want)

Ah, makes sense... I should have figured that.
For the graphing one... yea you lost me there. I can multiply it out but after that...

 

[xforeverxmetalx]

well, whatever works

Studying via spamming a forum apparently works.

 

[Nidan]

WARNING: math ahead

Ah, makes sense... I should have figured that.
For the graphing one... yea you lost me there. I can multiply it out but after that...

to get the extrema of a function you need the first and second derivation ( f'(x) and f''(x) )
the first has to be zero, while the second mustn't (f'(x) = 0, f''(x) != 0)
so first get all possible x by solving the first, then inserting these x into the second. if you get a value above 0 you have a minimum, below 0 its a maximum

 

[Nidan]

Studying via spamming a forum apparently works.

how was your final?

 

[xforeverxmetalx]

WARNING: math ahead

to get the extrema of a function you need the first and second derivation ( f'(x) and f''(x) )
the first has to be zero, while the second mustn't (f'(x) = 0, f''(x) != 0)
so first get all possible x by solving the first, then inserting these x into the second. if you get a value above 0 you have a minimum, below 0 its a maximum

If you say so.

 

[xforeverxmetalx]

how was your final?

Good, got an 82% :]

 

[xforeverxmetalx]

Hm... I wonder if they have an online German I class. If so, I might just take it, for the easy credit

 

[Nidan]

Good, got an 82% :]

congratulations

 

[xforeverxmetalx]

Aw, doesn't look like it. Too bad

 

[xforeverxmetalx]

congratulations

Thanks :]

 

[Nidan]

*Schandmail*

 

[xforeverxmetalx]

So far next semester, I'll probably take economics, anthropology, some sort of psychology, and something else. Probably English.