@CalvinKhor Hi

I'm getting the option (1)

But they say the correct answer is option (2).

Can you please explain the discrepancy?

@JohnRennie Hi

Hi :-)

Hello

I know the correct one is $E = cB$ but I get confused every time. Can you help me in not making those mistakes again?

@KnightadmiresChappo I don't think there's an easy way to remember that except that for an EM wave the electric field is much stronger than the magnetic field.

busy, sry

As in we almost never have to consider the magnetic field of an EM wave because its behaviour is dominated by the electric field.

@CalvinKhor No problem. Ping me with explanation, when you get free :)

@JohnRennie Can you please explain that sir? How electric field is stronger than B field?

I will say I have no idea what "y'' = \frac{2b} \\" is supposed to mean

ttyk

ttyl*

@KnightadmiresChappo it's just something you need to know.

@JohnRennie :) lol

@CalvinKhor I'm sorry it is $ y' = \frac{1}{2b}$

@JohnRennie Sir, do you know about Mr. Joseph Conrad?

@KnightadmiresChappo the author?

Yep

English Author (yesterday I asked about the Irish author and you didn't like that, lol)

@JohnRennie

To be honest I only read science fiction and fantasy

oh

I encounter real life every day so I don't want to read about it as well. When I read I want to read about something that is not real.

Those words are really very knowledge-ful.

for x≠0, xy''=y' iff xy'' - y' = 0 iff (y'/x)' = 0 iff y'/x = C iff y'=Cx iff y= Cx^2/2 + D so you get a two parameter family of solutions as you expect when you have two derivatives

and knowledge-ful is likely not a word

@CalvinKhor Was my solution incorrect?

@CaptainBohemian Hi, glad to have you here my friend.

@CalvinKhor For $C = \frac{1}{2b}$ and $D = -b$ we will get the original given equation. How you have solved the differential equation? I want to learn it :) ?

(I know separation of variables, substation and linear equation but only for first order)

@CalvinKhor knowledgeful is a word, I wrote it that way to add emphasis.

Incredible. I stand corrected and mildly perturbed that such a word exists. I know not why I do not like the word

Your solution is incorrect because it has extra solutions, those where C and D are not as you said

I wrote the full working out there. It’s just one of many tricks, using product / quotient rule ‘in reverse’

You could have gotten the same with an integrating factor since it is a first order equation for y’

At least, I presume it is ‘incorrect’ due to such a reason.

@CalvinKhor I still haven’t understood why my answer was wrong. Can you please give me a one more try?

What new thing could I say if you give me zero feedback on what I said?

@CalvinKhor Okay, I can see that you solved that second order differential equation and got an equation involving x and y (with two unknown parameters).

And I assigned values to those parameters, and we got the original equation given in the question. So, why my solution is incorrect?

^^^ I couldn’t understand that statement, especially “those where C and D are not as you said”

A first order ODE will only have one constant. I don’t know what kind of silly rules your exam has. But I would guess that constant should be b. Or something equivalent to it. If you have to make a choice to reduce two arbitrary constants into one constant, it’s probably ‘not the expected answer’.