form 2 ge maths...

2007-12-27 11:20 pm

1. Factorize 25h^2-(h^2+8h+16) .點計到個answer係 8(3+2)(-1) .
2.Volum of the cubid : 2(x+1)^3-12(x+1)^2+18(x+1) , the base of a cubiod is a square with sides of (x-2)cm each , the height of the cubiod : 2(x+1)cm
(a) If the side of a square is equal to the height of the cubiod,the area of the square is (Ax^2+Bx+c)cm^2.Find the values of A,B and C.

回答 (1)

Chun Ying

2007-12-27 11:45 pm

✔ 最佳答案

1. 25h^2-(h^2+8h+16)
= (5h)^2 - (h + 4)^2
= (5h + h + 4)(5h - h - 4)
= (6h + 4)(4h - 4)
= [2(3h + 1)][4(h - 1)]
= 8(3h + 1)(h - 1)

2. "If the side of a square is equal to the height of the cubiod" , then x - 2 = 2(x + 1)
x計出來係負數.......係咪抄錯?

3. Let BC = 3k and CD = 5k
2(3k + 5k) = 19.2
k = 1.2
therefore, BC = 3.6 and CD = 6

As triangle ABE is isoscles, therefore AB = AE
By Pyth.Theorem, 2AB^2 = BE^2
2AB^2 = 36
AB^2 = 18
AB = 3開方2

Area is the pentagon
= 1/2(AB)^2 + CD * BC
= 1/2(3開方2)^2 + 3.6 * 6
= 9 + 21.6
= 30.6 cm^2

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