maths(F.2)

a) 9x^2 + 30x + 25 <----- 係咪+25啊
= (3x)^2 + (2)(5)(3x) + (5)^2
= (3x+5)^2

b) 6x^2 + 10x
= 2x(3x+5)

c) 9x^2 + 30x + 25 - 6x^2- 10x
= (3x+5)^2-(6x^2+10x)
= (3x+5)^2-2x(3x+5)
= (3x+5)(3x+5-2x)
= (3x+5)(x+5)

2007-10-30 15:15:13 補充：
你地 form 2 咪教左(a b)^2 = a^2 2ab b^2 咁倒轉黎用咪變左a^2 2ab b^2 = (a b)^2 囉then 9x^2 30x 25 = (3x 5)^2跟住b個條重易 唔洗用上面個方法 直接抽個common factor出黎6x^2 10x=(2x)(3x) (2x)(5) = 2x(3x 5) 2因為 2x times 3x = 6x^2 , 2x times 5 = 10x 咁c 個條就用番a 同 b 既ans 代入去做就得

(a)
(2x+3)(2x+3) 2. 4(3x-5)上面係2次方 3. 2(5x-3y)(-3y+5x) 4. 求恆等式(2x+B)x-1(Ax-1)(x+1)中常數A及B的值。 ... 4x^2+12x+9. 2.4(3x-5)^2 =4(9x^2-30x+25) OR 36x^2-120x+100 ...
(b)
(2x)<(x+5)+(2x)>=40 (x ... 2x^2 10x 4x^2=40. 2x^2 4x^2 10x=40. 6x^2 10x=40. 6x^2 x=40-30. 6x^2 x=10 ... (x+5)+(2x)>(2x) =x>-5. 由於(x+5)+(2x)>=40. x>-5>=40.
故x>=35