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Mathematics 23 Online
OpenStudy (anonymous):

Local behavior questions! picture attachment below!

OpenStudy (anonymous):

@jim_thompson5910 hey! you helped with my other questions, any chance you know about this stuff too?

jimthompson5910 (jim_thompson5910):

f(x) = x^3 - 6x^2 what is f ' (x) ?

OpenStudy (anonymous):

hmm im not sure..you dont plug in 0 do you?

jimthompson5910 (jim_thompson5910):

have you learned about derivatives?

OpenStudy (anonymous):

that word doesnt sound familiar but i think we have!! hah

jimthompson5910 (jim_thompson5910):

is this calculus class?

OpenStudy (anonymous):

no it is classified as advanced algebra but it sure seems like calculus material. i just did the problem, would the answer be D?

jimthompson5910 (jim_thompson5910):

this is definitely an unfair problem if you haven't learned about calculus and derivatives

OpenStudy (anonymous):

yes ive never taken any calculus class. this material is all new.

jimthompson5910 (jim_thompson5910):

but we can at least use the graph

OpenStudy (anonymous):

yes thats what i did!

jimthompson5910 (jim_thompson5910):

notice how the graph continues on forever as you go down the left side so there is NO global min

jimthompson5910 (jim_thompson5910):

at the same time, the graph continues on forever as you go up the right side so there is NO global max

jimthompson5910 (jim_thompson5910):

there are no global extrema

jimthompson5910 (jim_thompson5910):

however, there is a peak at x = 0 so this is where the local max is there is a valley at x = 4 which is where the local min is

jimthompson5910 (jim_thompson5910):

there are no global extrema but there are 2 local extrema (1 local max and 1 local min)

OpenStudy (anonymous):

ahh so it would be B. i have a hard time telling the difference between global and local max/min.

jimthompson5910 (jim_thompson5910):

global refers to the entire domain unless otherwise explicitly stated

jimthompson5910 (jim_thompson5910):

local is just within a very specific interval (usually a small interval)

jimthompson5910 (jim_thompson5910):

yes B

OpenStudy (anonymous):

thank you! i have some others, would you be able to check my answers? if you dont have time thats fine!

jimthompson5910 (jim_thompson5910):

sure I can do that

OpenStudy (anonymous):

awsome! thank you. here is another. im not positive on my answer.

OpenStudy (anonymous):

its just telling you to find the polynomial function that goes with the graph. i know the leading coefficient cant be a negative number so that left me to A and B.

OpenStudy (anonymous):

actually im positive it must be A! i just checked again.

OpenStudy (anonymous):

lol forget about that. i dont know why im so stupid. okay i will send you the next one that im actually unsure about!

jimthompson5910 (jim_thompson5910):

choice A is correct

jimthompson5910 (jim_thompson5910):

you aren't stupid

OpenStudy (anonymous):

haha i may not be stupid but i was just acting stupid! i should have known. thank you though. here is one i am unsure about. you have to factor first right?

OpenStudy (anonymous):

im bad with these types of questions where you have to factor.

jimthompson5910 (jim_thompson5910):

yes factor as much as you can

jimthompson5910 (jim_thompson5910):

tell me what you get

OpenStudy (anonymous):

hmm 2x^2(6+x) (-6+x)?

jimthompson5910 (jim_thompson5910):

very good

jimthompson5910 (jim_thompson5910):

you can also write it as 2x^2(x+6)(x-6)

jimthompson5910 (jim_thompson5910):

2x^2(x+6)(x-6) = 0 2x^2 = 0 or x+6 = 0 or x-6 = 0 solve each equation for x

OpenStudy (anonymous):

Okay, so now the answer i get would be B! it has to be because 2x^2=0 is going to be 0 and it is going to be touch. and there are still the other two equations so it has to be B right?

jimthompson5910 (jim_thompson5910):

correct

jimthompson5910 (jim_thompson5910):

even multiplicity ----> touch odd multiplicity ----> cross

OpenStudy (anonymous):

perfect thanks! and this is the last one. im pretty sure im right, just want to make sure though.

jimthompson5910 (jim_thompson5910):

did you graph this function?

OpenStudy (anonymous):

i did. it only has one turning point

jimthompson5910 (jim_thompson5910):

yes, notice how it peaks out at (12.5, 156.25) this is the highest the graph goes...for the ENTIRE domain. So this is both a local max and a global max

jimthompson5910 (jim_thompson5910):

there is no local min or no global min because it continues on forever downward

OpenStudy (anonymous):

ohhh okay. so the answer would be D.

jimthompson5910 (jim_thompson5910):

good

OpenStudy (anonymous):

thank you!! you explained it really well. that was the last question i was unsure about! thank you again!

jimthompson5910 (jim_thompson5910):

no problem

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