中三數學題 help 急！20分 需列明步驟 plz!!

33.
3^(x+4) + 3^x = 82/9
(3^x)(3^4) + 3^x = 82/9
81(3^x) + 3^x = 82/9
(81+ 1)(3^x) = 82/9
82(3^x) = 82/9
3^x = 1/9
3^x = 1/3^2
3^x = (3^-2)
x = -2

答案 B -2

26.
圓錐體體積 V = 1/3 (pi)(r^2) h
r = 半徑, h = 高度
r/h = k (常數,不變)
r^2/h^2 = k^2
r^2 = k^2h^2
V = 1/3 (pi)(r^2) h
V = 1/3 (pi)(k^2)(h^2) h
V = 1/3 (pi)(k^2)h^3
1.331 V = 1/3 (pi)(k^2)H^3
1.331[h^3] = H^3
H^3 = 1.33h^3
H =( 1.331)^(1/3)h
H = 1.1h
h增加10%

答案 B 10%

27.
假設角DCB = x, 角ACB = x
角ACB = 角ABC = 2x (二等邊三角形 AC = AB)
三角形CDB, 66度 + x + 2x = 180度
3x = 180度 - 66度 = 114度
x = 114/3 = 38度
角ACB = 角ABC = 2x = 76度
角CAB = 180度– 76度- 76度 = 28度

答案 A 28°

36.
x^3 - (x + 2y)^3
X^3 – Y^3 = (X –Y) (X^2 + XY +Y^2)
x^3 – (x + 2y)^3 = {x – (x + 2y)} {x^2 + x(x + 2y) +(x + 2y) ^2}
x^3 – (x + 2y)^3 = {x – x - 2y} {x^2 + x^2 + 2xy + x^2 + 4xy +4y^2}
x^3 – (x + 2y)^3 = - 2y{3x^2 + 6xy +4y^2}

答案 C -2y(3x^2 + 6xy + 4y^2)




2012-01-30 05:47:36 補充：
26.
H^3 = 1.331h^3
H =(1.331)^(1/3)h
H = 新的水高度, h = 最初水的高度
(1.331)^(1/3), 求 1.331 的立方根 = 1.1
H = 1.1h
(1.1h - h)/h (100%)= 10%
h增加10%

27題圖有點小 不過聰明的你 應該看得出來!

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