calculus problem

[NA97GT]

There seems to be a few svt peeps who are good at calculus, I would not consider myself one. Can you guys help me with a problem I'm having.

suppose f(x)= (-3x^5)-(40x^3)+20

Algebraically find all critical values (stationary points),
intervals where f(x) is increasing and decreasing
and coordinated of relative maxima and minima.

Im confused bbecause this function seems to be constantly decreasing, so how would I express these valuse if they dont all exist?

 

[F the V-TAC]

Hmm....
To find the critical values, I think you need to find f'(x) and set it =to 0 or something... those are critical values I believe, and the points on the x plane where f(x) changes from increasing to decreasing....don't take my word for it though. A few months ago I woulda been able to answer this a lot better, but as soon as I took my AP Calc test I purged it from my brain

 

[PureStang]

taken from my notes from calc.

a) find f'(x). set equal to 0 solve to find critical numbers. place critical numbers on number line. use non-critical numbers in original equation to determine if final outcome is negative or positive. (so in this problem, -1 would be positive, so a positive would be placed in the (-infinity, 0) bracket). repeat for as many gaps you have (in this case 2 more times).

b) find where sign changes, if it goes + to -, its a local max and visa versa.

hope this helps a little.

 

[Blown_By_You]

Mother of god I don't miss that shit.. its only been two years and I've forgotten it all...

 

[Chris _Scott]

first you find f'(x) as stated above

set it to zero, and those are the critical values [since you dont have anything in a denominator, these would be ALL your possible critical values]

these are all the x-coordinates at which your graph has a 'hump' or changes from increasing to decreasing, or vice versa..IF it does

the values wheres f'(x) is positive is where its increasing, and negative where its decreasing

hope that helps, im too lazy to actually work it out

 

[PureStang]

Mother of god I don't miss that shit.. its only been two years and I've forgotten it all...

this is the stuff i love. lol. i got a 98% on the test that had this material. lol. im just too lazy since i worked a 9.5 hr day today...that and school isnt in...lol

 

[F the V-TAC]

damn am I proud of myself! I was correct in my lazy terms

 

[NA97GT]

taken from my notes from calc.

a) find f'(x). set equal to 0 solve to find critical numbers. place critical numbers on number line. use non-critical numbers in original equation to determine if final outcome is negative or positive. (so in this problem, -1 would be positive, so a positive would be placed in the (-infinity, 0) bracket). repeat for as many gaps you have (in this case 2 more times).

b) find where sign changes, if it goes + to -, its a local max and visa versa.

hope this helps a little.

Thank you that is helpful.
My main issue is that your function is a parabola, where mine is a decreasing line with a negative slope. Thus I dont have any intervals.

 

[txyaloo]

Thank you that is helpful.
My main issue is that your function is a parabola, where mine is a decreasing line with a negative slope. Thus I dont have any intervals.

You obviously haven't graphed it. (-3x^5)-(40x^3)+20 is definitely not a straight line. I graphed it and can see an inflection point at around (0,20). Remember the rules for finding inc/dec and min/max.

Work the process, and you'll get the right answer.

 

[NA97GT]

You obviously haven't graphed it. (-3x^5)-(40x^3)+20 is definitely not a straight line. I graphed it and can see an inflection point at around (0,20). Remember the rules for finding inc/dec and min/max.

Work the process, and you'll get the right answer.

Thanks for the advice, im still working on that.

 

[jerrad]

Sit next to a smart kid. You can "check" your answers.

 

[txyaloo]

Thanks for the advice, im still working on that.

Did you graph it yet? I find that helps visualizing the inflection/critical points. Either way, the process for finding min/max, inc/dec, is straight forward. Take the derivative. Find the critical values. Do the first/second derivative test.

 

[SVTburnout]

frig ill bite, ill do the math and scan my process if you want...

i got it almost worked out right now, and txyloo's spot on.

graphing works wonders.

gimme 15 mins and ill have it.

 

[SVTburnout]

im having trouble uploading my work, its just on a pad of graph paper with pencil..

fell free to PM me to compare awnsers... calc isnt really my forte, discreet is... but im + i got this one.

-gus

 

[txyaloo]

frig ill bite, ill do the math and scan my process if you want...

i got it almost worked out right now, and txyloo's spot on.

graphing works wonders.

gimme 15 mins and ill have it.

You're at 25 mins. :lol:

 

[SVTburnout]

took me 10 to figure it out, 15 to decide my scanner is effed. :bored:

and i was in b4 u :rockon:

 

[silverstang23]

just solve for x and plug it in to find y

 

[HYBRED]

I remember knowing how to do that once...

 

[txyaloo]

just solve for x and plug it in to find y

Not even close.

 

[SVTburnout]

just solve for x and plug it in to find y

:lol: