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Mathematics 14 Online
OpenStudy (anonymous):

solve the following for x...

OpenStudy (anonymous):

\[\frac{ f(x) - (-33) }{ x - 0 }\]

OpenStudy (anonymous):

f(x) = \[f(x) = 36xsin(17x) + 306\sqrt{3}x^2 -33\]

OpenStudy (anonymous):

x=0

OpenStudy (anonymous):

\[\frac{ f(x) - (-33)}{ x-0 } = f'(x)\]

OpenStudy (anonymous):

that is the derivative formula at x=0; X=0 is your answer

OpenStudy (anonymous):

is it? the answers says that x = 5Pi/102 and 7Pi/102

OpenStudy (anonymous):

alright Plug in either 5pi/102 or 7pi/102 in f(x) and see if you get -33.

OpenStudy (anonymous):

the original question was find the x coordinates of all points on the curve \[y = 36xsin(17x) + 306\sqrt{3}x^2 -33\] with a domain of \[\frac{ \Pi }{ 34 } < x < \frac{ 3\Pi }{ 34 }\] where to tangent line passes through the point P(0, -33)

OpenStudy (anonymous):

so im not sure if the rise/run formula is the right thing to do

OpenStudy (anonymous):

also the point (0, -33) is actually not on the curve, but this line is touching points of the curve somewhere

OpenStudy (anonymous):

which is where answer x= 5Pi/102 and 7Pi/102 comes from

OpenStudy (anonymous):

alright. let's see if we can write the equation of the tangent line

OpenStudy (anonymous):

maybe?

OpenStudy (anonymous):

with one m being rise/ivrun and the other m being the derivativer equate the two toeeach other

OpenStudy (anonymous):

dont think it works though

OpenStudy (anonymous):

yea the derivative is not defined at 0

OpenStudy (anonymous):

m = m \[\frac{ f(x) - (-33) }{ x - 0} = f'(x)\] \[\frac{ (36xsin(17x) + 306\sqrt{3}x^2 -33) - (-33) }{x } = 612xcos(17x) + 36\sin(17x) + 712\sqrt{3}x\]

OpenStudy (anonymous):

i tried doing this but im still not getting the correct answer

OpenStudy (anonymous):

did you try getting f'(x), maybe i did it wrong

OpenStudy (anonymous):

is the x^2 in the square root?

OpenStudy (anonymous):

no

OpenStudy (anonymous):

oh, then I was doing it all wrong... let me start over

OpenStudy (anonymous):

the slope is 0; you just have to use the x in the denominator to cancel the xs in the numerator and take the limit of that as x approaches 0

OpenStudy (anonymous):

so take the limit after the rise/run formula after you factor it?

OpenStudy (anonymous):

of the rise/run*

OpenStudy (anonymous):

yea

OpenStudy (anonymous):

this gives you the slope, and then what do you do to get the answer

OpenStudy (anonymous):

\[\lim_{x \rightarrow0}36\sin(17x) + 306\sqrt{3}x^2\]

OpenStudy (anonymous):

slope equals to 0, and then...?

OpenStudy (anonymous):

0 = f'(x) 0 = \[0 = 612xcos(17x) + 36\sin(17x) + 712\sqrt{3}x\]

OpenStudy (anonymous):

maybe solving for x here would be the answer?

OpenStudy (anonymous):

the answer is 5pi/102

OpenStudy (anonymous):

oh did you get it?

OpenStudy (anonymous):

and 7pi/102... you took the derivative wrong

OpenStudy (anonymous):

oh..

OpenStudy (anonymous):

you shouldn't have 712, its 612

OpenStudy (anonymous):

what is f'(x)?

OpenStudy (anonymous):

ohh

OpenStudy (anonymous):

and set them equal as you did before, 36sin(17x)+306(3)^(1/2)x=36sin(17x)+612xcos(17x)+612sqrt(3)x

OpenStudy (anonymous):

solve for x, and thats what you get?

OpenStudy (anonymous):

\[36\sin(17x)+306sqrt(3)x=36\sin(17x)+612xcos(17x)+612\sqrt(3)x\]

OpenStudy (anonymous):

yea, x= (1/102)(12*k*pi+5pi) or x = (1/102)(12*k*pi-5pi)

OpenStudy (anonymous):

n is an integer, pick n so that x is between pi/34 and 3pi/34

OpenStudy (anonymous):

oh ok, thanks!

OpenStudy (anonymous):

np

OpenStudy (anonymous):

whats n?

OpenStudy (anonymous):

hold on a second I will attach a file soon

OpenStudy (anonymous):

there you go

OpenStudy (anonymous):

on the pdf file, it should not be 5pi + or - 12kpi; it should be 5pi+12kpi or x=-5pi+12kpi since cos(-a)=cos(a); it is 2kpi + or - a with a being 5pi/6 in our case... any questions??

OpenStudy (anonymous):

what is k?

OpenStudy (anonymous):

I used k instead of n; its the same thing

OpenStudy (anonymous):

oh ok

OpenStudy (anonymous):

when you isolated for k , what are you finding

OpenStudy (anonymous):

is that like the period

OpenStudy (anonymous):

no; im trying to find k. x should be in a certain range. so if x is between pi/34 and 3pi/34 then (pi/34)<x<(3pi/34). this will help you find an interval for k so that your x is in the right range or domain if you want to call it that... now k should be an integer so you look at the interval of k and decide which integers are inside that interval... if you do this for 12kpi-5pi; you should get k=1... pi/34<=(1/102)(12kpi-5pi)<=3pi/4... try it

OpenStudy (anonymous):

ok i finally got it

OpenStudy (anonymous):

thanks for your help!

OpenStudy (anonymous):

np...

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