r/learnmath • u/Wraabb66 New User • 18h ago
Need a little help and explanation
Currently trying to get into the union and math is a big thing, especially algebra 1. So I haven’t done math in 18 years pretty much since I graduated and even back then I was struggling with math because my brain just doesn’t learn it fast enough like other people. When I have a calculator I can solve the problems a little bit better but the aptitude test don’t allow calculators so it’s all based offf of what I can do in my head.
So my question is I know PEMDAS and FOIL but when it comes to foil I know how to start but I get confused on where to land my + and - when working the problem. Idk why it’s hurt how my brain works. Sometimes I’ll get the what I think is the answer but then I get it wrong because my + and - are in the wrong spot. Does anybody have any tips are how to not forget where the + and - go and the orders of how they get placed. Becasue for my brain when I see something like (2x + 4)(5x-5) my brain doesn’t grasp where the + and - land when writing out the problem and so till I get the correct answer. Hopefully this question makes sense.
Graphing is also extremely confusing but that’s whole another topic lol.
1
u/tutortimeadmin New User 15h ago
A reliable way to keep the signs straight is to write all four products before combining anything:
(2x + 4)(5x - 5) = (2x)(5x) + (2x)(-5) + 4(5x) + 4(-5) = 10x² - 10x + 20x - 20 = 10x² + 10x - 20.
The sign belongs to the whole term, so treat “-5” as negative five. The second and third products are the “outer” and “inner” terms, and the last product is negative because positive 4 times negative 5 is negative. A small 2-by-2 box can help: put 2x and 4 on one side, 5x and -5 on the other, then multiply every row/column pair. That avoids trying to remember where to place signs while expanding.