# Simultaneous equation

#### Monkeyseat

##### Full Member
Hi,

I don't know what I'm doing wrong here, I've tried this several times and I'm apparently getting the wrong answer.

This is the equation:

I got y = -2 and x = 2. The book says the answer is x = 2 1/2 and y = -1 3/4.

Why do my answers work in this equation? I've tried numerous methods and keep coming up with the same answers. Here's what I did:

I've tried other methods like eliminating y and I still get the same. I also tried re-arranging it differently. If you can stick to elimination.

Please help and tell me where I am going wrong ASAP (need to know for tomorrow if you can). Maybe it was the re-arranging? I just multiplied the bottom of the fraction on both sides.

Excuse the handwriting.

Thank you very much.

#### rahidz2003

##### New member
Quite frankly, I think you're right

If x = 2.5 and y = -1.75, then the second equation becomes

(2.5-7)/(2*-1.75+3)=
(-4.5)/(-3.5+3)=9

So I'm guessing the book's wrong.

#### Monkeyseat

##### Full Member

Odd, when I checked it with their answer before I got 5 lol. Have I re-arranged them correctly? I've tried a few other ways like eliminating y and always get the same.

The book is sometimes wrong but so am I so I just want to check if anyone did get a different answer.

Many thanks.

#### Subhotosh Khan

##### Super Moderator
Staff member
Monkeyseat said:
Hi,

I don't know what I'm doing wrong here, I've tried this several times and I'm apparently getting the wrong answer.

This is the equation:

I got y = -2 and x = 2. The book says the answer is x = 2 1/2 and y = -1 3/4.

Why do my answers work in this equation? I've tried numerous methods and keep coming up with the same answers. Here's what I did:

I've tried other methods like eliminating y and I still get the same. I also tried re-arranging it differently. If you can stick to elimination.

Please help and tell me where I am going wrong ASAP (need to know for tomorrow if you can). Maybe it was the re-arranging? I just multiplied the bottom of the fraction on both sides.

Excuse the handwriting.

Thank you very much.
You checked -- excellent and you are correct.

Book's answers are wrong - if you use those you'll see that those do not check with the original equations.

#### Monkeyseat

##### Full Member
Yeah they both seem to be wrong with their answers. I must have just made a typo when checking them (well I think on the first). My answers are right from the original equation aren't they not just the re-arranged bit (which did I also do the correct technique?)? I know you said it's right but I was just wondering about that.

Still thank you very much for clarifying. I did check with my answers if that's what you mean but it's really annoying when the books make mistakes which I've seen countless times. :x Doesn't help when I mess up checking their answers lol. XD I don't even know how the heck they got that answer. Much appreciated.

By the way Subhotosh Khan I have not forgotten about the HCF/LCM thread, I have just been very busy and not had any time to get around to it (it wasn't work just something I was wondering about) so I do apologise but I will sort it out soon, maybe in a couple of days. Just so busy. If you have clarified again it's much appreciated.

Thank you both.