HELP!! Does this make any sense?!
http://mhf4u1.pbworks.com/w/page/26838563/Application%20Problem

- anonymous

HELP!! Does this make any sense?!
http://mhf4u1.pbworks.com/w/page/26838563/Application%20Problem

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- anonymous

THIS part!!

##### 1 Attachment

- anonymous

i dont understand how they got that :(

- Loser66

What don't you get?

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## More answers

- anonymous

how did they get b/w 9-13 necklaces ??

- Loser66

the intersections between the graphs|dw:1436711669825:dw|

- anonymous

no but i graphed it and the points were 3 and 19

##### 1 Attachment

- Loser66

|dw:1436711704284:dw|

- anonymous

yes

- Loser66

and between 9 and 13, parabola is higher than the line right?

- Loser66

that is the revenue > the cost, right?

- Loser66

@freckles please help me to finish the explanation. I have to go now.

- anonymous

isnt the parabola higher at 3-19?!

- anonymous

PL HELP!!!

- anonymous

@misssunshinexxoxo

- misssunshinexxoxo

@jim_thompson5910

- anonymous

i think it should be "steph should make 3-19 necklaces each week"

- anonymous

maybe the website is wrong?!??! because it doesnt make sense to me otherwise :(

- freckles

\[25n-n^2>55+3.5n \\ 0>n^2+3.5n-25n+55 \\ n^2-21.5n+55<0 \\ 10n^2-215n+550<0 \\ 2n^2-43n+110<0 \\ \text{ this does give } n \in (3,19)\]

- freckles

oops \[n \in [3,19]\]

- freckles

wanted to but brackets there to show to include the endpoints

- freckles

since actually you have the lower endpoint is approximately n=2.97 and the upper endpoint is 18.53
so you could actually say the answer is [3,19)
didn't include the 19 because 18.53 is less than 19
but definitely include the 3 since 3 is more than 2.97

- freckles

it looks like there was some dyslexia happening there on the website though :p

- anonymous

omg so i was right?! its b/w 3-19 ?

- anonymous

not 13-9?

- freckles

yep the weird thing is they even put the right answer after they said the wrong answer

- anonymous

yeah thats what got me confused

- anonymous

thanks a ton though!!
:)

- freckles

np

- anonymous

@freckles FRECKLES!!! How did you get

- anonymous

n∈[3,19]

- anonymous

??

- freckles

well actually n in [3,19) since 19 is a little greater than the actual left endpoint

- anonymous

where did you get the points 3,19? from the graph? or did you get that from the 25n-n^2>55+3.5n??

- freckles

\[2n^2-43n+110<0 \\ 2n^2-43n<-110 \\ n^2-\frac{43}{2}n<-55 \\ n^2-\frac{43}{2}n+(\frac{43}{2} \frac{1}{2})^2<-55+(\frac{43}{2} \frac{1}{2})^2 \\ (n-\frac{43}{4})^2<-55+\frac{43^2}{4^2} \\ (n-\frac{43}{4})^2<\frac{-55(16)+43^2}{16} \\ (n-\frac{43}{4})^2<\frac{969}{16} \\ \sqrt{ (n-\frac{43}{4})^2}< \sqrt{\frac{969}{16}} \\ |n-\frac{43}{4}|<\frac{ \sqrt{969}}{4} \\ - \frac{\sqrt{969}}{4}

- freckles

I solve the quadratic inequality I had above

- anonymous

so how'd you get 3 and 19 from all that?!

- freckles

calculator to approximate both the 43/4-sqrt(969)/4 and 43/4+sqrt(969)/4

- anonymous

sorry im being so difficult, i just really dont understand :(

- freckles

\[\frac{\sqrt{969}}{4}+\frac{43}{4} \approx 18.5322 \\ \frac{43}{4}-\frac{\sqrt{969}}{4} \approx 2.96781\]

- anonymous

ohhhhhhh alright

- anonymous

thank you soo so so much omg

- freckles

\[2.96781

- freckles

or an interval notation [3,19)

- freckles

in roster notation {3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18}

- freckles

by the way when we say n in [3,19) we should also include where n is a whole number (or you can say integer or whatever )

- freckles

lol just trying to be really proper with all the math terminology :p

- anonymous

so is it 3

- anonymous

** \[3\le n \le 19\]

- freckles

well I put \[3 \le n < 19\]
since 19 isn't actually included

- freckles

where n is integer of course

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