Why it's incorrect?

Question

Why it's incorrect?

jpsmarinho · Answer

attachment

anonymous · Answer

Is that suppose to be xy=cot(xy)?

jpsmarinho · Answer

I think so. My cotan(x) is equals to 1/tangent of x

jpsmarinho · Answer

^^

anonymous · Answer

which is the incorrect part?

anonymous · Answer

the part in green?

jpsmarinho · Answer

yes

anonymous · Answer

Well, I don't think the error is in the green but rather you made a mistake when differentiating: the derivative of cotangent is negative cosecant SQUARED, not just negative cosecant.

jpsmarinho · Answer

aah right, it's true. But in the green part, don't remain y' to isolate...

anonymous · Answer

yeah, you need to isolate y'

anonymous · Answer

to obtain a y'= blah blah format

jpsmarinho · Answer

So, it's incorrect to divide xy' + y to xy' + y ?This is my doubt, because, from what I know, it's correct.

anonymous · Answer

It is incorrect because if you are divide by xy' + y, you lose all instances of y' and therefore cannot solve for it.

anonymous · Answer

You are trying to solve for y', right?

anonymous · Answer

Solving for y' (which is dy/dx)

jpsmarinho · Answer

thank's @nolastudent for your help!

anonymous · Answer

No problemo!

anonymous · Answer

Who gave you this problem.
$$
u = \cot(u)
$$

is a set of countable number of points.

Just draw the function 
y=u and
y=cot(u)
They only intersects in a countable number of points.

jpsmarinho · Answer

This is a problem of Stewart's textbook.

jpsmarinho · Answer

unfortunately I don't have a software that plot implicit equations. This is advanced calculus?