-5/6 + -8/9 =

$$\begin{array}{l} \left(-\frac{5}{6}\right) + \left(-\frac{8}{9}\right)\\ The\;problem\;here\;is\;that\;we\;need\;a\;common\;denominator.\\ To\;fix\;this,\;let's\;multiply\;the\;first\;fraction\;by\;\frac{3}{3}\; and\;the\;second\;fraction\;by\;\frac{2}{2}.\\ This\;will\;give\;us\;a\;common\;demoninator\;(bottom\;number)\;of\;18.\\ \left(\frac{-5}{6}\times\frac{3}{3}\right) + \left(\frac{-8}{9}\times\frac{2}{2}\right)\\ \left(\frac{-15}{18}\right) + \left(\frac{-16}{18}\right)\\ Now\;that\;we\;have\;a\;common\;demoninator,\;we\;can\;add\;these\;fractions.\\ \left(\frac{-31}{18}\right)\\ So,\;that's\;our\;answer.\;You\;could\;also\;write\;this\;as\;a\;mixed\;number\;like\;so:\\ -1\frac{13}{18}\\ \end{array}$$

Hi Ninja,

Another way to write words is with a message box     \mbox{This will be a comment}

I saw heurika use some other command for a message but this is the one i use.  

You cannot put any maths things inside the parenthenses LaTex will not accept it.

Thanks Melody.

I see Alan did a similar thing..but it looks like he did two dolar signs? I'm not sure, here's his post on this: http://web2.0calc.com/questions/find-the-average-slope#r5

Alan is here so he can tell us!  Please Alan.

I actually don't think that Alan's $ signs did anything.

If you are working with LaTex away from a forum you need to put $ signs around the maths made parts.

On forums this is effectively done for you.  I know Alan writes a lot of his Latex and coppies it over.  He probably didn't here but the $ signs would just be a habit that he is in.

I don't know why he has put the 2 extra dollar signs at the front.  I think he would b e happy to tell us though.

This was your code Alan

$$$\int dx$

$$$\int dx$$ $

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The other day Heureka used something else instead of \mbox{} 

It had the same purpose.  I cant remember what it was but it would be referred to in the LaTex thread for sure. I have been faily consciencious about updating and adding to the LaTex thread.  Although I will admit that it is a bit of a mess.  

NinjaDevo sent me a message about this.  Here's a copy of the reply I sent him:

The default for the LaTeX box on the site is to be in "Display" math mode. I often switch this off to begin with by inserting $$ right at the start. If I then type words it comes out as text. 

In the "average slope" case I wanted to start with some "Inline" math, which requires a single $ immediately before and immediately after the math (so it looks like I started the whole thing with 3 dollar signs - 2 to switch off the default "Display" mode and 1 to switch on the "Inline" mode). 

Putting $$ immediately before and after the math produces "Display" mode math, where the math appears centred on a new line. 

You switch off math mode and enter text mode by using either $(for "Inline" math) or$$ (for "Display" math). 

Hope this helps. 
PS I'm no LaTeX expert - I just use trial and error and see what results!

I'll have to play with this.

So you use the $$ instead of using \mbox then ? You don't have to turn it off at the end then?

Doesn't matter I shall have to play.