幫幫手化簡呢2條方程式~~急!!!

a^2+2(2b-c)a-12b^2+20bc-8c^2
= a^2 + 2(2b-c)a + (2b-c)^2 - [12b^2 - 20bc + 8c^2 + (2b-c)^2]
= (a+2b-c)^2 - (12b^2 - 20bc + 8c^2 + 4b^2 - 4bc + c^2)
= (a+2b-c)^2 - (16b^2 - 24bc + 9c^2)
= (a+2b-c)^2 - (4b - 3c)^2
= (a + 2b - c + 4b - 3c) (a + 2b - c - 4b + 3c)
= (a + 6b - 4c) (a - 2b + 2c)

84x^2-271x+195
= 84(x^2 - 271x/84 + 195/84)
= 84[x^2 - 2 x (271/168) + (271/168)^2] + [195/84 - (271/168)^2]
= 84[(x - 271/168)^2 - 7921 / 28224]
= 84[(x - 271/168)^2 - (89/168)^2]
= 84[(x - 271/168 - 89/168) (x - 271/168 + 89/168)]
= 84 (x - 360/168) (x - 182/168)
= 84 (x - 15/7) (x - 13/12)
= (84 7 12) (7x - 15) (12x - 13)
= (7x - 15)(12x - 13)

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2009-04-16 19:35:11 補充：
除號又顯示不了 :

= (84 ÷ 7 ÷ 12) (7x - 15) (12x - 13)

= (7x - 15)(12x - 13)

第二題
(7x - 15) (12x - 13)

第一題
sorry