Can someone explain where I've gone wrong

[Dofusplayer567]

Why when I solve this simultaneous equation in a certain way, one of the two solutions disent present itself

 

[lev888]

You lost solution y=0 when you divided both sides by y.

 

[Steven G]

Can you please post your work so it is oriented correctly?

 

[Dr.Peterson]

Here it is, cleaned up a bit:


You should know better than to divide by y; that assumes that y is not zero.

Instead, when you have y^2 = 3y, collect terms on one side and factor.

 

[JeffM]

You lost solution y=0 when you divided both sides by y.

I'd prefer to say that the solution y = 0 was assumed away rather than lost.

 

[Steven G]

An immediate problem is saying that (3,3) is an intercept. EVERY x -intercept has y=0 and EVERY y-intercept has x=0. So I doubt very highly that (3,3) is an intercept.

 

[lev888]

An immediate problem is saying that (3,3) is an intercept. EVERY x -intercept has y=0 and EVERY y-intercept has x=0. So I doubt very highly that (3,3) is an intercept.

Should be 'intersect'.

 

[Steven G]

0^2 = 3*0 !!

Factor instead of dividing by an unknown
y^2-3y=0
y(y-3) = 0
y=0, y=3

 

[MarkFL]

Can you please post your work so it is oriented correctly?

That seems to happen with certain mobile devices, through no fault of the user. Here is a revised image:

 

[Steven G]

Should be 'intersect'.

Yep

 

[JeffM]

We are getting a bit off-topic, but I suspect "intercept" is ok here as a verb. "Intercept" as a noun is almost unknown outside mathematics and has a narrow, well-defined meaning in mathematics. Of course, I agree that "intersect" is a better choice of word in a mathematical context, but the technical meaning of "intercept" quite obviously derives from using "intercept" as a synonym for "intersect." The y-intercept is where a curve or line intercepts (intersects with) the y-axis.

 

[Dofusplayer567]

So when doing random simealtenous equations with lines I'm unsure of, how often should I be assuming y or x = 0. I'm assuming this a rare enough occurrence but. (also apologies for the spelling/grammar I am heavily dyslexic)

 

[lev888]

So when doing random simealtenous equations with lines I'm unsure of, how often should I be assuming y or x = 0. I'm assuming this a rare enough occurrence but. (also apologies for the spelling/grammar I am heavily dyslexic)

No need to assume that. Just when simplifying don't divide by a variable, factor it out instead.

 

[Deleted member 4993]

So when doing random simealtenous equations with lines I'm unsure of, how often should I be assuming y or x = 0. I'm assuming this a rare enough occurrence but. (also apologies for the spelling/grammar I am heavily dyslexic)

In general, you should NOT assume the value of a variable (be it zero, 1, 3.73 or any other number).

 

[Dofusplayer567]

brill. Thanks a lot all. This was bugging me for so long

 

[Dr.Peterson]

So when doing random simealtenous equations with lines I'm unsure of, how often should I be assuming y or x = 0. I'm assuming this a rare enough occurrence but. (also apologies for the spelling/grammar I am heavily dyslexic)

Did you ask this because of Jomo's comment in #6?

An immediate problem is saying that (3,3) is an intercept. EVERY x -intercept has y=0 and EVERY y-intercept has x=0. So I doubt very highly that (3,3) is an intercept.

That was not a comment about something you should assume, but about the word "intercept", which he took in a different way than you intended it. An x-intercept has y=0, but there is no x-intercept in your problem.