Results 1 to 4 of 4

Math Help - Foil Method

  1. #1
    Newbie
    Joined
    Dec 2008
    From
    Wellington ,FL
    Posts
    19

    Lightbulb Foil Method

    I know that is first,outer, inner, last but are there other ways to solve using the method?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    Joined
    Dec 2008
    From
    Scotland
    Posts
    901
    Quote Originally Posted by Russian View Post
    I know that is first,outer, inner, last but are there other ways to solve using the method?
    Ermmm what do you mean exactly?

    If you have a expression  (a+b)(c+d) , then you could re-write it as  a(c+d) + b(c+d) , and calculate from there.

    So for example:

     (x+5)(x-3)
    = x(x-3)+5(x-3)
    = x^2-3x+5x-15
    = x^2+2x-25

    Essentially, it's the same as foil method. Essential, all ways of expanding the expression are very close to foil method. Can't really go wrong :P.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor

    Joined
    Apr 2005
    Posts
    14,973
    Thanks
    1121
    Quote Originally Posted by Russian View Post
    I know that is first,outer, inner, last but are there other ways to solve using the method?
    To multiply together two expressions, you multiply every term of the first by every term of the last. "FOIL" is just a way of being sure you get all of them and only apply to "two terms times two terms".

    For example: to multiply (a+ b)(c+ d) I can use "FOIL": "First" terms, ab; "Outside terms", ad; "Inside" terms, bc; "Last" terms, bd. Adding all of those: ab+ ad+ bc+ bd.

    I could have got the same result by using the rule: Multiply the first term in the first expression, a, by each of the terms in the second expression: a(c+ c)= ac+ ad. Then multiply the second term in the first expression by each of the terms in the second expression: b(c+ d)= bc+ bd. Adding those: ac+ ad+ bc+ bd, exactly as above.

    If I have 3 terms in, say, the first expression, like (a+ b+ c)(u+ v), I can't use "FOIL" exactly but I can think:
    Multiply the first term in the first expression, a, by every term in the second expression- a(u+ v)= au+ av.
    Multiply the second term in the first expression, b, by every term in the second expression- b(u+ v)= bu+ bv.
    Multiply the third term in the first expression, c, by every term in the second expression- c(u+ v)= cu+ cv.

    Now add all of those: (a+ b+ c)(u+ v)= au+ av+ bu+ bv+ cu+ cv.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Dec 2008
    From
    Wellington ,FL
    Posts
    19

    Talking

    Quote Originally Posted by HallsofIvy View Post
    To multiply together two expressions, you multiply every term of the first by every term of the last. "FOIL" is just a way of being sure you get all of them and only apply to "two terms times two terms".

    For example: to multiply (a+ b)(c+ d) I can use "FOIL": "First" terms, ab; "Outside terms", ad; "Inside" terms, bc; "Last" terms, bd. Adding all of those: ab+ ad+ bc+ bd.

    I could have got the same result by using the rule: Multiply the first term in the first expression, a, by each of the terms in the second expression: a(c+ c)= ac+ ad. Then multiply the second term in the first expression by each of the terms in the second expression: b(c+ d)= bc+ bd. Adding those: ac+ ad+ bc+ bd, exactly as above.

    If I have 3 terms in, say, the first expression, like (a+ b+ c)(u+ v), I can't use "FOIL" exactly but I can think:
    Multiply the first term in the first expression, a, by every term in the second expression- a(u+ v)= au+ av.
    Multiply the second term in the first expression, b, by every term in the second expression- b(u+ v)= bu+ bv.
    Multiply the third term in the first expression, c, by every term in the second expression- c(u+ v)= cu+ cv.

    Now add all of those: (a+ b+ c)(u+ v)= au+ av+ bu+ bv+ cu+ cv.

    thank you again
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Help with Foil Method
    Posted in the Algebra Forum
    Replies: 2
    Last Post: November 22nd 2009, 02:42 PM
  2. FOIL method
    Posted in the Algebra Forum
    Replies: 3
    Last Post: August 24th 2009, 06:24 PM
  3. How to foil this equation...
    Posted in the Algebra Forum
    Replies: 2
    Last Post: January 12th 2009, 04:23 PM
  4. Do I use FOIL?
    Posted in the Algebra Forum
    Replies: 7
    Last Post: June 17th 2008, 11:39 AM
  5. Help with FOIL
    Posted in the Algebra Forum
    Replies: 5
    Last Post: June 10th 2008, 10:28 AM

Search Tags


/mathhelpforum @mathhelpforum