Currently have the first 3 answers here to start us off, not sure where to go from here, please help! (problems: http://imgur.com/Eo8fZIR,mJ2vS04,3ys9vme,xyjbOve ) here's what i've got:
* A=40
* B=20
* C=12 hour period

- anonymous

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- katieb

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- anonymous

What exactly is the question?

- anonymous

There's multiple questions, would you like me to type them out for you? I don't mind.

- anonymous

Are there more than the 3 in the link? Or are you just asking if those answers are correct?

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## More answers

- anonymous

There are more than 3, I have the first 3 which I listed and I need assistance with the rest, I believe the answers for the first 3 that I got are vital to answering the rest.

- anonymous

There are 5 more questions, 2 bonus questions but i'm not too worried about them.

- anonymous

ok. I didn't see the links to the other questions before

- anonymous

Oh it's alright, you've got it or do I need to type them?

- anonymous

I see them.

- anonymous

For part d,
a is the amplitude and
b is 2π divided by the period
The y = cos x parent function has a maximum on the y-axis. Your function has the minimum there, so make "a" negative

- anonymous

so for A, the amplitude was either 40 or 20 from the previous questions, correct?

- anonymous

The amplitude is 20, the answer from B

- anonymous

I didn't have my work pulled up sorry about that, so it's y=20 cos 2pi x?

- anonymous

Wait! I read you wrong, a=20 and b=2pi/the period?

- anonymous

close. you need to divide 2π by the period of 12 and make the amplitude negative to account for the reflection
\[y=-20\cos \frac{ 2\pi }{ 12 }x\]

- anonymous

Am I going to need to get this down to one number for the answer to "a=" or will it be an equation?

- anonymous

Or will this be for both a= and b=

- anonymous

oh you're right. They are asking for a and b separately

- anonymous

so a will be -20 and b will be π/6

- anonymous

Does that make sense?

- anonymous

That does, I was wondering when the negative 20 would come in as I looked around online and saw that it would turn out like that, now the next question is to "sketch" and label a graph, Seeing as we can't really do that here, what would I put into my graphing calculator to figure this out?

- anonymous

Not sure if the draw option is any use, im new here

- anonymous

We could use this: https://www.desmos.com/calculator

- anonymous

ok

- anonymous

so you want to enter the equation we found above. and set your window to show 1 period at least

- anonymous

so your horizontal axis should be from 0 to 12. and vertical from -20 to 20

- anonymous

y=-20 cos 2pi/12x is the equation I want to put in?

- anonymous

Reduce the 2π/12 to π/6 and use parentheses to avoid ambiguity
y=-20 cos (pi/6)x

- anonymous

Hold up, put everything after cos in ().
y=-20 cos ((pi/6)x)

- anonymous

Have this so far, should I fix it with the ()'s? http://imgur.com/ptftpkN

- anonymous

Yes

- anonymous

If I add the extra parenthesis it makes two lines, like this: http://imgur.com/KM6VOZB

- anonymous

Is that what we want?

- anonymous

yes. If you zoom out you'll see the waves

- anonymous

Yes! alright so that's all that was? we're done graphing?

- anonymous

yes.

- anonymous

Mind sticking around and helping with the rest? I'll give you medals or whatever the currency on here is.

- anonymous

oh yeah. I just meant we were done with that question

- anonymous

Alright so F, how do we find the average water levels?

- anonymous

Just the top of the waves?

- anonymous

It's the average of the maximum and minimum, which I think was 32 and 12. I need to go back to the beginning to check

- anonymous

52 and 12 I believe

- anonymous

you're right

- anonymous

So what can we do with those to find the average? Divide?

- anonymous

Add them and then divide
(52+12)/2 = 22

- anonymous

Crazy how complicated they make it sound and then it's that easy! This next one may be a bit of a challenge

- anonymous

I have the graph on hand, how do I determine where the times are?

- anonymous

That's where the first column comes in. 11:15 is 2 hours after 9:15, so you want to find y when x = 2.

- anonymous

will finding y give the water level?

- anonymous

correct!

- anonymous

not sure how to find it with just x, walk me through it?

- anonymous

yes. It might actually be easier to do this on a calculator than to use the graph. For the first one, plug in 2 for x.
y = -20 cos ((π/6)*2)
http://www.wolframalpha.com/input/?i=-20+cos+%28%28%CF%80%2F6%29*x%29+at+x+%3D+2

- anonymous

so for each one we just plug in the hours and we get the level, for this it's -10?

- anonymous

right

- anonymous

3:45pm is 7 hours, right?

- anonymous

6.5 hrs

- anonymous

19.31?

- anonymous

yes

- anonymous

and then 6:15 is 9 hours? I'm in high school I should really be able to tell time at this point but it's hard without a clock to look at.

- anonymous

lol. It is 9. I'm just as pathetic. I have to count it on my fingers

- anonymous

wolfram just gave me the answer as "true", that cant be right

- anonymous

copy your link here

- anonymous

http://www.wolframalpha.com/input/?i=y+%3D+-20+cos+%28%28%CF%80%2F6%29*9%29

- anonymous

Just take out the y= so it will evaluate the expression

- anonymous

0?

- anonymous

yep

- anonymous

for the next one it's looking like we're working backwards, it gives us the water level but not the time, how do we manage this?

- anonymous

Use 7 for y and solve for x.
7 = -20 cos ((π/6)*x)

- anonymous

http://www.wolframalpha.com/input/?i=7+%3D+-20+cos+%28%28%CF%80%2F6%29*x%29?

- anonymous

8.5 hours?

- anonymous

or 7.5

- anonymous

http://www.wolframalpha.com/input/?i=7+%3D+-20+cos+%28%28%CF%80%2F6%29*x%29%2C+0%3Cx%3C12

- anonymous

sorry about that. You have to restrict the domain to just the period, or it will give all possilbe answers

- anonymous

this is looking like jibberish to me, is it 12? i'm seeing 12 a lot in there

- anonymous

hold up. can we go back to part c for a second?

- anonymous

the 12 hour period, yes

- anonymous

The period is actually 24. (9:15 to 3:15 is only half the period)

- anonymous

9:15 to 3:15 is a six hour gap. so six hours from low to high plus 6 hours from high back to low is a 12 hour period, right?

- anonymous

ok. yes. massive brain fart

- anonymous

so is H a 12 hour period as well?

- anonymous

yes, so there will be two solutions over the 12 hour period

- anonymous

Ignore all the "alternate form" gibberish and scroll down to where it says "solutions"
You may have to click on the "approximate form" box
http://www.wolframalpha.com/input/?i=7+%3D+-20+cos+%28%28%CF%80%2F6%29*x%29%2C+0%3Cx%3C12

- anonymous

Do you see x = 8.32 and x = 3.68?

- anonymous

I see them now yep, what do they have to do with it?

- anonymous

that equals 12?

- anonymous

no, they are the x values where the water level is 7

- anonymous

and they helped us determine that it's a 12 hour period in some way I guess?

- anonymous

The other way around. The equation 7 = -20 cos ((π/6)*x) has infinitely many solutions. We used the 12 hour period to restrict the amount of solutions the equation would give us. That's why the 0

- anonymous

got it!

- anonymous

So to find the times for H, add 3.68 hrs and 8.32 hrs to 9:15.

- anonymous

20.115

- anonymous

not sure how to add .___ in time

- anonymous

9:15 is 9.25 hours
9.25 hrs + 3.68 hrs = 12.93 hr (pm)
convert 0.93 hrs to minutes by multiplying by 60 → 55.8 minutes
First time 12:56 pm

- anonymous

wait a minute are we still on H or have we moved onto the bonus questions? I'm getting lost in all these times here as I know 9am is involved in both

- anonymous

I thought we were still on H

- anonymous

No this is still H

- anonymous

I was showing you how to add the times.

- anonymous

The first time we got for H was 3.68 hours. We need to add that to 9:15 to get the time of day the question is asking for

- anonymous

that makes much more sense, and when you did that you got 12.93, correct? should we round this?

- anonymous

With 12.93, we have to convert the decimal part to minutes, because there's no 12:93 on a clock. That's why I multiplied 0.93 by 60 to get 55.8, and I rounded that to 56 minutes

- anonymous

So it's only a 56 minute period?

- anonymous

no

- anonymous

12 hours 56 minutes

- anonymous

12:56 is the time at which the water level is 7

- anonymous

got it now, thanks for the description, it's okay if you dont want to do the bonus questions but if you're up for the challenge I am as well

- anonymous

give me a sec.

- anonymous

sure

- anonymous

If the low tide repeats every 12 hours, there will be 3 in a 24 hour period, inclusive.
|dw:1433136689393:dw|

- anonymous

and 2 high tides

- anonymous

and you can go off that same chart to get both? I'd think so since high and low are both on there

- anonymous

yes you can

- anonymous

Well I gave you best response which I guess gave medals, is there anything else I can give you? very thankful you stuck around to help

- anonymous

No I think that's it :)

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