need help on the attachment

- anonymous

need help on the attachment

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- anonymous

##### 1 Attachment

- anonymous

come on no has helped you with this yet?

- anonymous

no

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## More answers

- anonymous

should i solve this or go to sleep.....

- anonymous

solve before going, please

- anonymous

Oops! forgot to sleep after going

- anonymous

okay, first things first, lets find the first derivaitve of the function your where given

- anonymous

can you find it?

- anonymous

9sec^(2)x

- anonymous

okay good

- anonymous

now can you please evaluate:
f(pi/4)=9sec^2(pi/4)

- anonymous

square root of 2

- anonymous

is it right?

- anonymous

basically to make it more accesible we can write this as:
f(pi/4)=9[sec(pi/4)]^2

- anonymous

further more we can write it as: f(pi/4)=9[1/cos(pi/4)]^2

- anonymous

then evalutaing we get:
f(pi/4)=9[1/sqrt(2)/(2)]^2

- anonymous

what square root 2/2???

- anonymous

further: f(pi/4)=9[sqrt(2)]^2
which the gives us: f(pi/4)=9(2), which is 18
Thus f(pi/4)=18

- anonymous

yes, look at the unit circle, at pi/4 or 45 degrees, cos is sqr(2)/2, now if we rationalize the numerator we get just sqrt(2)

- anonymous

oh, thought your doing sec

- anonymous

i rewrote secx as 1/cosx

- anonymous

how come?

- anonymous

just to make is easier for me, but if realise that sec(pi/4) is sqrt(2) then more power to you

- anonymous

Now we have found the slope (m) of our line, it is 18

- anonymous

y-y=m(x-x)

- anonymous

yes, but we will use this form, y=mx+b

- anonymous

i am getting sleepy lets finish this problem

- anonymous

ok

- anonymous

what would be the b in the slope formula

- anonymous

Now remeber we said, that we have the x coordinate in the beining of pi/4, lets evaluate the orginal function at this point, this will give us the y in our line.
f(pi/4)=9tan(pi/4)
=9(1)
=9
now we have our x which is pi/4, we have our slope which is 18, lets plug this info into our line:
9=18(pi/4)+b
this means that b is = to 9-18pi/4

- anonymous

now lets substitute everyting in:
y=18x-(36-18pi)/(4)

- anonymous

are we good?

- anonymous

36??

- anonymous

i combined 9 and 18pi/4

- anonymous

yes?

- anonymous

still don't see how you can 36??

- anonymous

|dw:1316152625201:dw|

- anonymous

you could've just simplify it to 9pi/2

- anonymous

okay, then smarty pants do it your way, regardless we came to a correct answer

- anonymous

sorry, so the finally would look like this 18x+9(1-pi/2)

- anonymous

sure

- anonymous

I just look the answer choices and so which one was the closest, but how come they have it 18x+9(1-pi/2) instead of just 18x+9pi/2

- anonymous

distribute the negative sign, first

- anonymous

huh?

- anonymous

what negative sign?

- anonymous

|dw:1316153351852:dw|

- anonymous

got it ?

- anonymous

but was there a 9-18pi/4 at the beginning

- anonymous

yes there was

- anonymous

can you not see it:
|dw:1316153548845:dw|

- anonymous

I meant why was 9-18pi/4 at the begginig

- anonymous

above i accidentally wrote:y=18x-(36-18pi)/(4), but is was really suppose to be :
y=18x+(36-18pi)/(4), sorry about the typo

- anonymous

okay, so can we lay this problem to rest?

- anonymous

I guess, but still don't get why they have 9-18pi/4 plug into b instead of just 18pi/4 by itself

- anonymous

- anonymous

|dw:1316153804630:dw|

- anonymous

oh, ok now we can lay this problem to rest, thanks so much for being patience

- anonymous

its good you ask questions, i know i can confusing sometimes :)

- anonymous

Thanks for giving me a metal

- anonymous

yeah I just want to understand the problem instead of just getting the answer

- anonymous

because I might see it on the test, but thanks again

- anonymous

anytime

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