I still want to get to simultaneous equations but I need to write a little more about rearranging equations. If you start with a+b=c, then if you want to make b the subject of the equation (this means that you want to know what b is) then you have to take a from both sides of the equals sign (see below for simple equations). If you want a to be the subject of the equation then take b from both sides, so a=c-b.

To put this mathematically, a+b=c, and a=c-b, and b=c-a.

The written explanation took five lines, the mathematical explanation took less than a line.

If you have the equation axb=c, there is a convention that says you don't need the x. If you have 10 lots of a you can write 10xa but it is easier and less confusing to write 10a. So in this example ab=c. If you want a to be the subject of the equation you have to divide both sides by b, so a=c/a. If you want b to be the subject then divide both sides by a, so b=c/a.

That sums it up.

## Sunday, 22 March 2009

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