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Mathematics 11 Online
OpenStudy (marcelie):

Help Please !!1

OpenStudy (marcelie):

OpenStudy (anonymous):

\[y\sin(3x)=x\cos(3y)\] right?

OpenStudy (anonymous):

diff wrt x get \[y'\sin(3x)+3y\cos(3x)=\cos(3y)-3xy'\sin(3y)\]

OpenStudy (anonymous):

btw your answer to 50 is a mistake

OpenStudy (marcelie):

oh okay ty . i fixed it lol . but ummm

OpenStudy (marcelie):

this is what i got for 51.

OpenStudy (marcelie):

|dw:1459908990747:dw|

OpenStudy (anonymous):

is it clear how to do this implicit diff?

OpenStudy (marcelie):

thats the dy/dx right ?

OpenStudy (anonymous):

yeah i mean how to find it

OpenStudy (anonymous):

how to get \[y'\sin(3x)+3y\cos(3x)=\cos(3y)-3xy'\sin(3y)\]

OpenStudy (marcelie):

yes thats gonna be this

OpenStudy (anonymous):

then replace \(x\) by \(\frac{\pi}{3}\) and \(y\) by \(\frac{\pi}{6}\) and solve for \(y'\)

OpenStudy (marcelie):

oh so then i plug it in directly?

OpenStudy (marcelie):

but question do i have to move some stuff ?

OpenStudy (anonymous):

you can use algebra to solve for \(y'\) first, but it is easier just to plug in the numbers, then solve

OpenStudy (marcelie):

oh okay so then when its implicit its better to plug it in directly ?

OpenStudy (anonymous):

\[y'\sin(3x)+3y\cos(3x)=\cos(3y)-3xy'\sin(3y)\] \[y'\sin(\pi)+3\frac{\pi}{6}\cos(\pi)=\cos(\frac{\pi}{2})-3\frac{\pi}{3}\sin(\frac{\pi}{2})\]

OpenStudy (anonymous):

i dropped a \(y'\) somewheres

OpenStudy (marcelie):

that was on the left side ?

OpenStudy (anonymous):

\[y'\sin(\pi)+3\frac{\pi}{6}\cos(\pi)=\cos(\frac{\pi}{2})-3\frac{\pi}{3}\sin(\frac{\pi}{2})y'\]

OpenStudy (anonymous):

but now it is easy, since \(\sin(\pi)=0\) and \(\cos(\pi)=-1\)

OpenStudy (marcelie):

oh okay so i got -1/2 ?

OpenStudy (anonymous):

also \(\cos(\frac{\pi}{2}=0\) and \(\sin(\frac{\pi}{2})=1\)

OpenStudy (anonymous):

\[-\frac{\pi}{2}=\frac{\pi}{2}y'\]

OpenStudy (anonymous):

oops another mistake damn

OpenStudy (anonymous):

\[-\frac{\pi}{2}=\pi y'\]

OpenStudy (anonymous):

so yeah, \(-\frac{1}{2}\)

OpenStudy (marcelie):

oh okay so then

OpenStudy (anonymous):

then you are done, unless you need the equation for the line

OpenStudy (marcelie):

yes the equation

OpenStudy (anonymous):

you got the point \((\frac{\pi}{3},\frac{\pi}{6})\) and you got the slope \(-\frac{1}{2}\) use the point slope formula

OpenStudy (marcelie):

|dw:1459909748070:dw|

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