不明白為什麼會這麼計方程,請教一下我!

a) 6[2x-3(x+1)]=2x-10
6(2x-3x-3)=2x-10
12x-18x-18=2x-10
12x-18x-2x=-10+18
-8x=8
x=-1

c) 2[(3x-4)+2x]=x+10
2(3x-4+2x)=x+10
6x-8+4x=x+10
6x+4x-x=10+8
9x=18
x=2

問題1:
為什麼a題的6[2x-3(x+1)] 乘左6後,變左12x-18x-18,點解兩個減號?不是12x-18x + 18??
sol
because negative number * possitive number is really equil to negative number
so 6[2x-3(x+1)]
=12x-18(x+1)
=12x-18x-18

問題2:
為什麼b題的2[(3x-4)+2x],乘左2後,變左6x-8+4x? 點解唔係好似a題咁樣:6x-8- 4x ??
such like q1
2[(3x-4)+2x]
=2(3x-4)+4x
=6x-8+4x

6[2x-3(x+1)]
2x(6)-(6)(3x+3)
12x-18x-18

2010-11-28 21:04:40 補充：
2[(3x-4)+2x]
2(3x-4)+2(2x)
6x-8+4x
10x-8
_________________________
2[(3x-4)+2x]
2(3x-4+2x)
2(5x-4)
10x-8