if bored...and decent in calculus....

[underguy77]

if you could give me a hand id really appriciate it. i missed a week of class....been sick as hell and i got a test tomorrow. My professor is some foreign guy and i cant understand him so i usually figure this stuff out on my own. im having a really hard time with this and if anyone is feeling up to doin some math problems and showing me what ya did (i got a TI 83 too so if u gotta use it just let me know what to hit) Id appriciate it

1) find the x-coordiates where the horizontal tangents for f(x)=2x^3-3x^2-19 occur. the rightmost one occurs....?

2) Let P(x,y)=ln(x^2y). Then Px(1,1) is...?

3)Suppose the marginal cost of producing x copies of a book is given by dy/dx=1000/y (squr root of X). if y = 200 when x = 4 then the cost of producing 625 books is...?

4) the supply and demand functions for a certain commodity are given by: supply: p=2+9x/4, and demand: p=13- x/2. then producers surplus is....?

and consumers surplus is...?

thats the types of questions that are gonna be on the test.....if anyone can help me out id appricate it very much

peace
underguy77

 

[fistfullofsteel]

at least you aren't taking trig. i hate trig.

 

[slickdadd]

#1. if im not mistaken, horizontal tangent lines are horizontal, and infinite and dont occur at any one x coordinate, making a right most coordinate non existant

 

[slickdadd]

#3. You have to relate y=200 when x=4. Simplify it by dividing both by four, where you get y=50 when x=1. Therefore y=50x. Plug in 625 to find out y for the problem, which comes out 31250. Plug in y and x into the original function and you get .00128, which i guess is the marginal cost. At least how i interpreted the equation. Which was 1000/(Y x X^(1/2)) 1/2 being the same as the square root.

 

[Norman Bates]

if you could give me a hand id really appriciate it. i missed a week of class....been sick as hell and i got a test tomorrow. My professor is some foreign guy and i cant understand him so i usually figure this stuff out on my own. im having a really hard time with this and if anyone is feeling up to doin some math problems and showing me what ya did (i got a TI 83 too so if u gotta use it just let me know what to hit) Id appriciate it

1) find the x-coordiates where the horizontal tangents for f(x)=2x^3-3x^2-19 occur. the rightmost one occurs....?

I think you meant the point where the horizontal touches the graph.
To be horizontal f´(x)=0 ( i think)
f´(x)= 6x^2-6x+0= 6x ( 6x-1)

first extrema: 6x=0 x=0
2nd extrema: 6x-1=0 x= 1/6

The most right touchpoint is the second extrema.

 

[Y_lifter]

The answer is 7:45 PM eastern...

Yea, ... that's when the train will arrive in New York...

Your Welcome bro.... anytime

 

[slickdadd]

Re: Re: if bored...and decent in calculus....

I think you meant the point where the horizontal touches the graph.
To be horizontal f´(x)=0 ( i think)
f´(x)= 6x^2-6x+0= 6x ( 6x-1)

first extrema: 6x=0 x=0
2nd extrema: 6x-1=0 x= 1/6

The most right touchpoint is the second extrema.

the graph doesnt cross the horizontal axis in the original function when the derivative equals zero, it just has no slope. It only crosses at one point.

 

[Norman Bates]

Re: Re: Re: if bored...and decent in calculus....

the graph doesnt cross the horizontal axis in the original function when the derivative equals zero, it just has no slope. It only crosses at one point.

I didn´t mean the axis, i meant when the differentiated graph becomes 0, cause that ought to be the point when the tangent is horizontal.
I don´t know the correct expressions in English but i hope people understand what i want to say nevertheless.

 

[underguy77]

thanks guys,
these problems are word for word off the sample exam that he gave us. in case anyone was wondering the answers are (or closest to)

1) 1

2) 2

3) 360

4) 18, 4.00

of course the answers dont help me that much when i dont know how to do the problems, but ive figured 2 of them out for now

fistfullofsteel- yeah I HATED trig
y-lifter lol.....u bastard!

i appriciate it guys