FOIL ProcedureDate: 8/13/96 at 22:20:31 From: Anonymous Subject: FOIL Procedure Hi! I am having problems with the F.O.I.L concept. I understand the procedure, it's just hard to remember. Got any hints? It is super tough to learn the negatives and positives. For example, how do I do (2X-5)(3Xsq-5x+4)? Date: 8/14/96 at 0:43:33 From: Doctor Paul Subject: Re: FOIL Procedure! The idea of FOIL is to make sure that each term in the first set gets multiplied by each term in the second set. Let's do an example with letters (not numbers). (A + B) * (C -D + E) We want to multiply each term in the second part (C, D, and E) by each term in the first part (A, B) The easiest way to go is just left to right. Pick the leftmost term in the first part (A) and multiply it by each successive term in the second part. We get: A*C + A*(-D) + A*E Then we add to this the next term in the first part times each of the terms in the second part.. A*C + A*(-D) + A*E + B*C + B*(-D) + B*(E) When we add it all together, we get: A*C - A*D + A*E + B*C - B*D + B*E Get the idea? Let's do a real example: (2x-5)(3x^2-5x+4) As seen above, we have: 2x*3x^2 + 2x*(-5x) + 2x*4 + (-5)*3x^2 + (-5)*(-5x) + (-5)*4 Let's multiply it out: 6x^3 - 10x^2 + 8x - 15x^2 + 25x - 20 Now we have two x^2 terms and two x terms. Let's combine them to get our final answer: 6x^3 - 25x^2 + 33x - 20 I hope this helps you out. If you have any more questions feel free to submit them to Dr. Math. Regards, -Doctor Paul, The Math Forum Check out our web site! http://mathforum.org/dr.math/ |
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