中一數 ` 2o點~

1.
6(2q - 1/3)(2 - q)

= (12q - 2)(2 - q)

= 12q(2 - q) - 2(2 - q)

= 24q - 12q2 - 4 + 2q

= -12q2 + 26q - 4

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2.
4(y - 2y)(3y + 2)

= (4y - 8y2)(3y + 2)

= 4y(3y + 2) - 8y2(3y + 2)

= 12y2 + 8y - 24y3 - 16y2

= -24 y3 - 4y2 + 8y

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3.
(3b -2b + 4)(5 - 6)

= (3b -2b + 4)(-1)

= -3b + 2b2 - 4

= 2b2 - 3b - 4

這一題的問題中，(5 - 6)可能有錯。

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4.
(x - 3)(x + 1)

= (x2 - 6x + 9)(x + 1)

= (x2 - 6x + 9)x + (x2 - 6x + 9)

= x3 - 6x2 + 9x + x2 - 6x + 9

= x3 - 5x2 + 3x + 3

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5.
2a(2a - 7b) - 2(3a - 4ab + 5)

= 4a2 - 14ab - 6a2 + 8ab - 10

= -2a2 - 6ab - 10

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6.
(3x + 2y) - (2x - 3y)

= (9x2 + 12xy + 4y2) - (4x2 - 12xy + 9y2)

= 9x2 + 12xy + 4y2 - 4x2 + 12xy - 9y2

= 5x2 + 24xy - 5y2
=

2008-10-19 15:22:20 補充：
3.
(3b - 2b² + 4)(5 - b)
= (3b - 2b² + 4)5 - (3b - 2b² + 4)b
= 15b - 10b² + 20 - 3b² + 2b - 4b
= 2b³ - 13b² + 11b + 20