A importância de saber a tabuada.
Autor: Romulo Mussel | Publicado: 2012-04-12T11:00:00-03:00

&nbsp; &nbsp; &nbsp; Para quem estuda Matemática saber a famosa tabuada de multiplicação é fundamental. Muitos teóricos discutem sobre esta questão, seria necessário mesmo decorar a tabuada, ou seria melhor entendê-la?
&nbsp; &nbsp; Digo que ambos são importantes, entender é fundamental, mas decorar é mais do que necessário. Pela experiência que tenho em sala de aula, os alunos começam a ter problemas quando aparecem as famosas contas de vezes e as de dividir, e este problema só é agravado porque os alunos não conhecem a tabuada de multiplicação, e quando não a conhecem, qualquer conta simples se torna tão trabalhosa que o aluno acaba por desistir. Vamos tentar entender a tabuada de vezes?

Veja a figura:

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&nbsp; &nbsp; &nbsp; &nbsp; Esta figura nos dá por exemplo o resultado de 4 x 5 = 20. Note que temos 4 linhas, cada uma contendo &nbsp;5 unidades da letra x. Uma figura semelhante a esta é a que segue:

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&nbsp; &nbsp; &nbsp; &nbsp;Repare que se virarmos a figura anterior teremos a mesma coisa, porém nesta temos 5 x 4 =20. Agora são 5 linhas, cada uma contendo 4 unidades da letra x.
&nbsp; &nbsp; &nbsp; &nbsp; Logo de início temos a lei da comutatividade, ou seja:

&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 5 x 4 = 4 x 5 = 20

&nbsp; &nbsp; Quando invertemos as parcelas de uma multiplicação o resultado é exatamente o mesmo. Esses entendimentos são fundamentais, mas imagine ter que fazer um monte de x para descobrir quanto é 9 x 8. Com certeza teremos dois problemas, o primeiro é o trabalho de escrever todos, o segundo é o de contar todos, qualquer uma das duas etapas feita de modo impreciso fará com que você erre o resultado. É interessante entender, e até fazer a figura para uma primeira vez, mas e depois, você não acha mais fácil decorar?
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Com a ideia da figura e com a comutatividade, temos que decorar apenas 36 casos.

2 x 2 = &nbsp; 4 &nbsp; 3 x 3 = &nbsp; 9 &nbsp;&nbsp;4 x 4 = 16&nbsp;&nbsp;&nbsp;5 x 5 = 25&nbsp;&nbsp;&nbsp;6 x 6 = 36&nbsp;&nbsp;&nbsp;7 x 7 = 49&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;2 x 3 = &nbsp; 6&nbsp;&nbsp;&nbsp;3 x 4 = 12&nbsp;&nbsp;&nbsp;4 x 5 = 20&nbsp;&nbsp;&nbsp;5 x 6 = 30&nbsp;&nbsp;&nbsp;6 x 7 = 42&nbsp;&nbsp;&nbsp;7 x 8 = 56&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;2 x 4 = &nbsp; 8&nbsp;&nbsp;&nbsp;3 x 5 = 15&nbsp;&nbsp;&nbsp;4 x 6 = 24&nbsp;&nbsp;&nbsp;5 x 7 = 35 &nbsp;&nbsp;6 x 8 = 48&nbsp;&nbsp;&nbsp;7 x 9 = 63&nbsp; &nbsp;&nbsp; &nbsp;2 x 5 = 10&nbsp;&nbsp;&nbsp;3 x 6 = 18&nbsp;&nbsp;&nbsp;4 x 7 = 28&nbsp;&nbsp;&nbsp;5 x 8 = 40&nbsp;&nbsp;&nbsp;6 x 9 = 54&nbsp; &nbsp;&nbsp; &nbsp;2 x 6 = 12&nbsp;&nbsp;&nbsp;3 x 7 = 21&nbsp;&nbsp;&nbsp;4 x 8 = 32&nbsp;&nbsp;&nbsp;5 x 9 = 45&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;2 x 7 = 14&nbsp;&nbsp;&nbsp;3 x 8 = 24&nbsp;&nbsp;&nbsp;4 x 9 = 36&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;8 x 8 = 64&nbsp; &nbsp; 9 x 9 = 812 x 8 = 16&nbsp;&nbsp;&nbsp;3 x 9 = 27 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;8 x 9 = 72&nbsp;&nbsp;2 x 9 = 18
&nbsp; &nbsp; &nbsp; &nbsp; Repare que não tem 5 x 4, mas tem 4 x 5 que é a mesma coisa. Também não tem 1 x 8, pois 1 x 8 = 8, assim como 1 x 9 = 9, 1 x 3 = 3 e assim por diante, a própria figura é bem simples, e não precisa ser decorada.&nbsp;&nbsp; &nbsp; Se você souber de cabeça essas 36 combinações, conseguirá resolver todos os problemas de multiplicação e de divisão com que se deparar.&nbsp; &nbsp; &nbsp; &nbsp; O que está esperando? Memorize estas combinações e depois confira fazendo as figuras.
Bons estudos!!!