A Strange Step-by-Step Solution

Earlier this evening I saw the following picture posted by Mathster (@mathstermaths)  

 
As I tweeted I am really not keen on the use of “move all terms to the left” as I don’t think it is clear what this is meant to mean mathematically. Indeed, it could easily lead to misconceptions with people thinking that you just move terms over an equals sign with no conceptual understanding of what should be happening. Stephen Cavadino (@srcav) has written about this here

I thought I would try going online and doing the same equation as is solved in the example. The step by step solution I obtained was even stranger: 

 
I have no idea why there are steps 1 and 2 simplifying the right hand and left hand side before the pointless step of rearranging to obtain everything equal to zero…….

Christine (@MissNorledge) also pointed out the strange behaviour this app shows when rounding. According to the example above 8/3 rounds to 2.666666666666665. To me this indicates poor use of floating poor arithmetic. 

Jasmina then showed something that is clearly a bug in their parsing library  

 I’m curious as to how this app is working, specifically

  • How the user input is being parsed?
  • Are they using a JavaScript symbolic algebra library (and if so which one)?
  • How is the “maths” implemented?

Unfortunately at a first glance the JavaScript viewable using the Safari developer options isn’t particularly illuminating. As I’m away for the weekend I haven’t been my able to delve very deeply into the code with a good editor like Sublime and work out what is doing what. 

The app can’t solve quadratics with complex roots or cubics: 

  

 All in all I want to know more about this…

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