• Changing RCF's index page, please click on "Forums" to access the forums.

Homework help...

Do Not Sell My Personal Information
This is using the chain rule, which states d/dx of (ax+b)^c is the derivative of the outside term multiplied by the derivative of the inside term.

It's a pain to get used to at first, but it will become on of the most common derivative rules you'll apply in calculus.
That explanation of the chain rule never made much sense to me because it implies that the derivative of f(x) = (ax+b)^c is equal to f'(x) = derivative of (ax + b) times the derivative of c... i like the u substitution explanation more where, in the case of (ax + b)^c, you rewrite it as u = ax + b and thus u^c then its dy/dx = dy/du x du/dx and you use the power rule c*u^c-1 (derivative of y with respect to u... in other words dy/du) multiplied by the derivative of u which is the derivative of (ax +b) (derivative of u with respect to x... in other words du/dx...
 
Last edited:
1. Find the velocity v and acceleration a of an object whose position s at time t is given by
s= 4.9t^2 =2t +4

2.Revenue Revenue sales analysis of a new toy by Toys Inc. indicates that the relationship between the unit price p and the monthly sales x of its new toy is given by the equation
p=9e^(-.04x)

3. The cost function and the demand equation for a certain product are
C(x)=18x+153
and
p=-3x+76
find the marginal value

4. Find derivative of
(x^4 e^x^4)
 
here's a seemingly easier one that probably deserves it's own thread for the debate that usually follows. Most people who get it wrong will never believe the explanation of why they are wrong. You are on a game show, there are 3 doors. Behind one door, there is a car. The game will work like this

step 1 - you pick a door
step 2 - the host shows you a door that you didn't pick that doesn't have the car
step 3 - you are given an option to switch from the door you picked to the one you didn't pick that the host didn't show you.

The question. Should you switch and does it matter?
 
here's a seemingly easier one that probably deserves it's own thread for the debate that usually follows. Most people who get it wrong will never believe the explanation of why they are wrong. You are on a game show, there are 3 doors. Behind one door, there is a car. The game will work like this

step 1 - you pick a door
step 2 - the host shows you a door that you didn't pick that doesn't have the car
step 3 - you are given an option to switch from the door you picked to the one you didn't pick that the host didn't show you.

The question. Should you switch and does it matter?

Why would you? You have a 1/2 chance either way. Wait. I remember this in HS. You swap. Not totally sure why though.
 
Last edited:
You make the switch. When you're originally picking you have a 1/3 chance of guessing correctly. That means that after swapping you have a 2/3 chance of guessing correctly.

Basically you can keep your one door or you can essentially swap it for the other 2, one of which will be removed leaving just the correct door.
 
You make the switch. When you're originally picking you have a 1/3 chance of guessing correctly. That means that after swapping you have a 2/3 chance of guessing correctly.

Basically you can keep your one door or you can essentially swap it for the other 2, one of which will be removed leaving just the correct door.

Yup. This question stumped some of the greatest mathematicians of our time when it came up. If I remember correctly, a savant working for a New York paper discussed this in a column, and people from both MIT and Oxford demanded she retract the claim. The believed the odds were 50/50, because the probability changes the second you reveal a wrong door. It took a series of computer simulations to bear out the real answer. To her credit, she stuck by it, despite the vitriolic response.

Here, I looked it up...

http://en.wikipedia.org/wiki/Marilyn_vos_Savant
http://en.wikipedia.org/wiki/Monty_Hall_problem
 
Yup. This question stumped some of the greatest mathematicians of our time when it came up. If I remember correctly, a savant working for a New York paper discussed this in a column, and people from both MIT and Oxford demanded she retract the claim. The believed the odds were 50/50, because the probability changes the second you reveal a wrong door. It took a series of computer simulations to bear out the real answer. To her credit, she stuck by it, despite the vitriolic response.

Here, I looked it up...

http://en.wikipedia.org/wiki/Marilyn_vos_Savant
http://en.wikipedia.org/wiki/Monty_Hall_problem

Apparently I'm more brilliant than some of the greatest mathematicians.



Or I just thought about it logically and didn't over think it. I'm awful at math.
 
1. Find the velocity v and acceleration a of an object whose position s at time t is given by
s= 4.9t^2 =2t +4

2.Revenue Revenue sales analysis of a new toy by Toys Inc. indicates that the relationship between the unit price p and the monthly sales x of its new toy is given by the equation
p=9e^(-.04x)

3. The cost function and the demand equation for a certain product are
C(x)=18x+153
and
p=-3x+76
find the marginal value

4. Find derivative of
(x^4 e^x^4)

1) So velocity is the change is position, or the slope of the function of position. So v = 9.8t - 2.
Acceleration is the change in velocity, so taking the derivative of the velocity equation yields a = 9.8.

2) Monthly change in sales at the price x will be p = -.36e^(-.04x). I can only assume that's what you're looking for.

3) Try this explanation: http://www.enotes.com/homework-help/price-demand-equation-cost-function-production-152057

4) You get (4x^3*e^x^4)+(x^4*4x^3*e^x^4) where the first part is from taking the derivative of x^4 and the second part is from the derivative of e^x^4. This simplifies to 4x^3*e^x^4*(x^4 + 1).
 
Yup. This question stumped some of the greatest mathematicians of our time when it came up. If I remember correctly, a savant working for a New York paper discussed this in a column, and people from both MIT and Oxford demanded she retract the claim. The believed the odds were 50/50, because the probability changes the second you reveal a wrong door. It took a series of computer simulations to bear out the real answer. To her credit, she stuck by it, despite the vitriolic response.

Here, I looked it up...

http://en.wikipedia.org/wiki/Marilyn_vos_Savant
http://en.wikipedia.org/wiki/Monty_Hall_problem

She stuck to her answer because she was right. The also is smarter than the MIT professor and others who wrote her.
 
Thanks drew, I ended up getting those.. just kicked a fucking shit ton of ass on this midterm except for one problem.. couldnt for the life of me figure it out..


Assume the following equation depicting the relationship between price and quantity demanded (x).

p= 100e^-.05x

What is the marginal cost if x=5?

Now. I spent 90% of my time on this question and still couldnt get an answer I felt comfy with. Firstly, youre supposed to find the derivative of the equation. (this is my first attempt). So that is basically 100e^-.05x (-.05). Thats the equation to find the derivative of an E equation.

I also tried flipping in 5 for the x term. This provided me with the closest answer available... it was like, 77.78 and the closest answer given was 77.68. Im sure this isnt the correct answer though.

What the hell am I missing??? Then, last idea, is that p(x) = R and youre supposed to find marginal revenue of that, which would be its' derivative. so this equals

100e^-.05x (-.05) times x =

i dint even fucking know what that answer is. That, theoretically, should be the answer. So what, 100e^-.05x^2 (-.05x^2) = 77.78 * (-.1x) which equals 77.78 * (-.5)? this is clearly not the right fucking answer. I.. i fucking give up
 
You make the switch. When you're originally picking you have a 1/3 chance of guessing correctly. That means that after swapping you have a 2/3 chance of guessing correctly.

Basically you can keep your one door or you can essentially swap it for the other 2, one of which will be removed leaving just the correct door.


this is actually brought up in the movie 21 (good movie). I have a degree in mechanical engineering and this really threw me for a loop. then again me and math occasionally disagree :mad:
 
Thanks drew, I ended up getting those.. just kicked a fucking shit ton of ass on this midterm except for one problem.. couldnt for the life of me figure it out..


Assume the following equation depicting the relationship between price and quantity demanded (x).

p= 100e^-.05x

What is the marginal cost if x=5?

Now. I spent 90% of my time on this question and still couldnt get an answer I felt comfy with. Firstly, youre supposed to find the derivative of the equation. (this is my first attempt). So that is basically 100e^-.05x (-.05). Thats the equation to find the derivative of an E equation.

I also tried flipping in 5 for the x term. This provided me with the closest answer available... it was like, 77.78 and the closest answer given was 77.68. Im sure this isnt the correct answer though.

What the hell am I missing??? Then, last idea, is that p(x) = R and youre supposed to find marginal revenue of that, which would be its' derivative. so this equals

100e^-.05x (-.05) times x =

i dint even fucking know what that answer is. That, theoretically, should be the answer. So what, 100e^-.05x^2 (-.05x^2) = 77.78 * (-.1x) which equals 77.78 * (-.5)? this is clearly not the right fucking answer. I.. i fucking give up

I think you made it too hard. You should find derivative of the function which should be -5e^-.05x. Then substitute 5 in for x to find the value of the derivative at the correct point which would be -3.894.
 
this is actually brought up in the movie 21 (good movie). I have a degree in mechanical engineering and this really threw me for a loop. then again me and math occasionally disagree :mad:

I think it's interesting that this seemed like common sense and logic to me, not math. I blow at math.
 
this is actually brought up in the movie 21 (good movie). I have a degree in mechanical engineering and this really threw me for a loop. then again me and math occasionally disagree :mad:

the thing that throws people off is it's teh fact that who knows what and when that changes the odds. If you pick the door in your head and keep it a secret, and then are shown a door that could be your secret door, then on the times your door isn't picked, it doesn't matter if you switch.

If hte person showing the door doesn't know where the car is, so will show the car 1/3 of the time, it doesn't matter if you switch.

It's only when the door you pick is known and an empty door has to be shown by someone who knows both your pick and the car location that it matters.

I spent hours trying to convince my father, who was pretty smart, of the correct answer. I even wrote a computer simulation (in hypercard) to prove it to him. Idon't think he ever quite believed it because he couldn't get past the fact that picking after the door is shown makes it 50-50.

Oh, and for the post above, the person who put this in Parade magazine wasn't a savant, her name was "vos Savant". SHe is the official world record holder for highest IQ. In all of the years she ran the column, she only gave the wrong answer once. That's why this problem became so talked about, when math experts where claiming she was wrong when she actually wasn't.
 
the answers given were like.. 77.68, 56 something, 61 something and 41 something.. I have not been able to get any of these answers and ive been working at this sonofabitch alld ay
 

Rubber Rim Job Podcast Video

Episode 3-13: "Backup Bash Brothers"

Rubber Rim Job Podcast Spotify

Episode 3:11: "Clipping Bucks."
Top