Question 8961
things like FOIL are some of my personal bugbears in maths and maths teaching.


Why spend time learning something like that when all you need know is what the hell you are supposed to be doing in the first place?


Right then:


you have 2 brackets
each bracket has 2 terms in it
each of the 2 terms in the first bracket needs to be multiplies with each of the 2 terms in the second bracket. Period!


As to the order you do this, it does not matter one jot! However, most people seem to take the first 9a and multiply it to the 2 terms in the second bracket and then take the second term (the -7) and multiply it to the 2 terms in the second bracket too.


So we end up with 4 terms, namely {{{(9a)*(9a) + (9a)*(7) + (-7)*(9a) + (-7)*(7)}}} --> written out long-windedly. This becomes:


{{{81a^2 + 63a - 63a - 49}}} which simplifies, in this case to


{{{81a^2 - 49}}}


jon.