F.3 maths

(4x+9)^2=(4x+9)(6x+13)
16x^2+72x+81=24x^2+52x+54x+117
8x^2+34x+36=0
4x^2+17x+18=0
(x+2)(4x+9)=0
x=-2,-2.25

2008-07-20 16:02:49 補充：
because:in equ,(x+2)=0,(4x+9)=0
therefore there are 2 answers, x=-2,-2.25

只有一個答案的是錯的

(4x+9)^2=(4x+9)(6x+13)
(4x+9) = (6x+13) <----兩邊除(4x+9)
9-13 = 6x-4x
-4= 2x
x=-2

(4x+9)2=(4x+9)(6x+13)
(4x+9)- (4x+9)(6x+13)=0
(4x+9)[1-(6x+13)]=0
4x+9=0 or 1-(6x+13)=0
x=-9/4 or x=7/3

2008-07-19 00:36:18 補充：
4x+9=0 or 1-(6x+13)=0
x=-9/4 or x=-2

(4x+9)^2=(4x+9)(6x+13)

(4x+9) = 0 <because is 4x+9=0, both sides would equal to zero>or 4x + 9 = 6x + 13

x = -2.25 or x = -2.5

so, no need to expand everything :)