唔識列方程,,help me!!

1)設長 = x cm , 則闊 = x - 3 cm2(x + x-3) = 342x - 3 = 17x = 10長 10 cm , 闊 = 10-3 = 7 cm
2)設祖父今年 x 歲 , 則家明今年 x/6 歲 ,(x - 9) - (x/6 - 9) = 60x - x/6 = 606x - x = 3605x = 360x = 72祖父今年 72 歲。
3)設原價是 x 元 ,35x = (35 - 10)(x + 120)35x = 25(x + 120)35x = 25x + 300010x = 3000x = 300每個花瓶原價 300 元。
4)設較長一段長 x cm ,則 三角形每邊長 x/3 cm , 正方形每邊長 x/3 - 4 cm ,即較短一段長 4(x/3 - 4)cmx + 4(x/3 - 4) = 403x + 4(x - 12) = 1203x + 4x - 48 = 1207x = 168x = 24較長一段長 24 cm
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(x/12 - 0.5)(15) = x[(x - 6)/12] (15) = x15(x - 6) = 12x15x - 90 = 12x3x = 90x = 30

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2.)
設祖父今年年齡為x,i.e.家明今年年齡=x/6
(x-9) - (x/6 - 9) = 60
5x/6 = 60
x/6 = 12
x = 72
所以祖父今年年齡 = 72
3.)
設花瓶原售價為$x,i.e. 款項 = $35x
35x/(x+120) = 35 - 10
35x = 25x + 3000
10x = 3000
x = 300
所以花瓶原售價為$300.
4.)
設較長1段鐵線長度為x cm,i.e. 較短1段長鐵線為(40-x)cm,
x/4 - 4 = (40-x)/3
x/4 - 4 = 40/3 - x/3
7x/12 = 52/3
7x/4 = 52
x = 208/7
所以較長1段的長度為208/7 cm
http://a367.yahoofs.com/hkblog/rDkOb8SWERnmmaR4UeTpiIbmgvVT_2/blog/20101129071726802.jpg?ib_____DELDAzKHK
(x/12 - 0.5)15 = x
5x/4 - 15/2 = x
x/4 = 15/2
x/2 = 15
x = 30
(x-6)(15)/12 = x
5(x-6)/4 = x
5x - 30 = 4x
x = 30

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