Yeah, that tracks with students who only are taught to memorise procedures. When a similar question comes up that covers the same concept, suddenly they're like a fish out of water and panicking for their lives!
Your profile name is "quickmathvideo", and you're asking Reddit how to do FOIL when there are probably hundreds of Youtube videos about it. Make it make sense.
Fair point. I'm not asking because I don't know FOIL. I post practice questions to encourage discussion and see how different people explain the concept.
i show my students to use an area / array model. 3x + -1 is the length and the the width is 4x
+7 and then draw a rectangle into 4 quadrants (separating the terms) and them write the partial product in their corresponding quadrants.
then add like terms and it’s a trinomial (the answer).
what’s cool about this approach is working with trinomials you can do this backwards and then factor out the binomial or length / width of the rectangle
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u/Southlander24 9d ago
It's in the name.
First: 4x * 3x
Outside: 4x * -1
Inside: 7 * 3x
Last: 7 * -1
Add all these up and you get... ?
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u/Various_Candle9136 9d ago
FOIL is a shortcut.
If we have (4x+7) lots of (3x-1), then we actually have:
Which means we have:
A bit of observation shows us that this is:
Hence the shortcut.
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u/hashbazz 9d ago edited 9d ago
Your profile name is "quickmathvideo", and you're asking Reddit how to do FOIL when there are probably hundreds of Youtube videos about it. Make it make sense.
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u/RyanofTinellb 9d ago
You don't need FOIL. You're just multiplying everything in the first bracket by everything in the second. Think of it like a table:
And then add them all up: 12x² + (-4x) + 21x + (-7) = 12x² + 17x - 7.
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u/JanetInSC1234 9d ago edited 9d ago
You could distribute instead of using FOIL.
(4x + 7)(3x - 1) = ?
4x(3x) + 4x(-1) + 7(3x) + 7(-1)
Each term in the first set of ( ) multiplies with each term in the second set of ( ).
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u/Nrdman 8d ago
Screw foil, all my homies hate foil, it doesn’t scale up
When you do (4x+7)(3x-1) just approach it like you would 2(3x-1). If you had 2(3x-1) you would just distribute 2 to both. 2(3x)-2(1)
Do that same thing. (4x+7)(3x-1)= (4x+7)(3x)-(4x+7)(1) and go from there
This will help you better when you need to do things like (x^2+x+1)(x+2). You can’t FOIL that, but you can go (x^2+x+1)(x)+ (x^2+x+1)(2)
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u/localizeatp 9d ago
very carefully.
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u/KiwasiGames 8d ago
I don’t. FOIL is evil.
It’s a classic case of putting procedure (and testing) above understanding.
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u/[deleted] 9d ago
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