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Q&A #6030

Teachers' Lounge Discussion: GCF & LCM factor trees

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From: Loyd

To: Teacher2Teacher Public Discussion
Date: 2002092605:30:22
Subject: Re: Math; What are factor trees?

What are factor trees? Factor trees are a way to express a composite number as a product of primes. For example, lets factor 72: 72 / \ 8 9 / \ / \ 2 4 3 3 / \ 2 2 Thus, 72 = 2 x 2 x 2 x 3 x 3. If the above stays in alignment, then that's it. I usually have algebra students write in a column form when trying to find factors of numbers such as 180: 1 x 180 2 x 90 (double first one and take half of the other factor) 3 x 60 ( triple first one and take 1/3 of the other factor) 4 x 45 (double 2nd one and take half of the other factor) 5 x 36 6 x 30 9 x 20 10 x 18 12 x 15 ( double the 6th one and half the other factor) That should do it since the next one will be 15 x 12. Thus, I use doubles and halves, triples and thirds, etc. The column method is not necessarly for finding a product of primes, but for factoring trinomial expressions in algebra of the form: ax^2 + bx + c. Of course, you may prefer to list the factors horizontial vice vertical. Someone expressed dissatisfaction with factor trees. They are are often a good way to factor. I don't believe there is a best way that everybody should teach. There is always more than one way to do something.

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