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標題:

F.2 Maths x4`

發問:

1)Factorize xy-4x-3y+12 2)Determine whether 1/4(x-2)(x-6) = (x/2 -2)^2 -1is an identity 3)Expand (4x^2 +9)(2x-3)(2x+3) 4)Expand (ab-5c)^2 thx`

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最佳解答:

1) xy - 4x - 3y + 12 = (xy - 4x) -(3y - 12) = x(y - 4) - 3(y - 4) = (x - 3)(y - 4) 2) L.S. = (1/4)(x - 2)(x - 6) = (1/4)(x2 - 8x + 12) = (x2/4) - 2x + 3 = (x2/4) - 2x + 4 - 1 = [(x/2)2 - 2(x/2)(2) + (2)2] -1 = [(x/2) - 2]2 - 1 = R.S. Hence, it is an identity. 3) (4x2 + 9)(2x - 3)(2x + 3) = (4x2 + 9)[(2x)2 - (3)2] = (4x2 + 9)(4x2 - 9) = (4x2)2 - (9)2 = 16x? - 81 4) (ab - 5c)2 = (ab)2 - 2(ab)(5c) + (5c)2 = a2b2 - 10abc + 25c2

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