In fact, do you know your multiplication tables well? In order to know for sure, draw a circle, write a number at the centre and on the circle write 10 numbers from 0 to 9 in any order. Example :
If you are able to go round the circle by giving the result of the 10 multiplications in less than 20 seconds, it means that you know the 7 times table very well. If you do not know the multiplication tables well, there is no use continuing with this lesson, you need to learn them ! (Learning the tables, 2nd grade lesson)
If you already know your tables, let's get back to the equations. The aim is to find x.
2x + 4 = 12
If we take away 4 from both sides, the equation is still valid. Therefore 2x + 4 - 4 = 12 - 4. Finally this gives us 2x = 12 - 4. In practice, we never write the intermediate step, we immediately write 2x = 12 - 4. In fact when we move a term to the other side of the = sign, we change the sign of that term. Examples :
See also : algebra on fmaths.com