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Mathematics 10 Online
Logic007:

Solve the following eqn

Logic007:

\(x\frac{dy}{dx}=cot~y\)

nuts:

do you know how to do this one?

nuts:

just rewrite as \(1/x \text{ dx}=\tan y \text{ dy}\) integrate \(\int dx/x=\int y dy\) super easy

Logic007:

Yes, I got \(y=cos(x+c)\) is it correct?

nuts:

one sec let me check

nuts:

I got something else, can you show what you did?

Logic007:

\(-In|cos~y|=In~x+c\) \(In|cos~y|^{-1}=In~x+c\)----> not really sure if we can do like this XD \(cos^{-1}y=x+c\) \(y=cos(x+c)\)

nuts:

should be -ln cos y = ln x + C ln (sec y) = ln x + C sec y = C*e^x

Logic007:

owh shouldn't it be \(In(sec~y)=Inx +C\) \(sec~y=x+e^C\) \(y=sec^{-1}(x+e^C)\)

nuts:

ln(sec y)=ln x +C e^(ln sec y)=e^(ln x +C) sec y = e^(ln x)*e^C sec y =C*e^ln(x) -> call e^C just C sec y = C*x You don't want to use the inverse trig function because that's not a real inverse, it will remove solutions from the relation that satisfies the equation I think

Logic007:

owh I c if we integrate \(\frac{1}{x}dx\) would it become \(In(x+C)\) or \(In(x)+C\)

nuts:

ln(x) + C the constant is always outside...

nuts:

just like if you integrate cos(x) you get sin(x)+C and not sin(x+C)

Logic007:

http://prntscr.com/m3awu8 shouldnt it be + ?

nuts:

because if you derive ln(x+C) you get 1/(x+c)

nuts:

no, read through it, e^(ln x +C)=e^(ln x)*e^(C)

nuts:

exponent law

Logic007:

\(\color{#0cbb34}{\text{Originally Posted by}}\) @nuts because if you derive ln(x+C) you get 1/(x+c) \(\color{#0cbb34}{\text{End of Quote}}\) owh,yes,dats right Thanks for clearing my thoughts XD

Logic007:

\(\color{#0cbb34}{\text{Originally Posted by}}\) @nuts no, read through it, e^(ln x +C)=e^(ln x)*e^(C) \(\color{#0cbb34}{\text{End of Quote}}\) owhhh, I c LOL *facepalm* Aite thanks bro

nuts:

yup no worries man, let me know if you have other questions!

Logic007:

Alright,will do! :D

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