✔ 最佳答案
好要步驟呀嘛(不過閣下自認非高人也^_^)
1. (2y-4)-(3y+1)
=2y-4-3y-1
=2y-3y-4-1
=(2-3)y-4-1←依步寫唔寫都得嘅
=-y-5
=-(y+5)←依步寫唔寫都得嘅
2. (3-6a)-(1-2a)
=3-6a-1+2a
=-6a+2a+3-1
=(-6+2)a+3-1←依步寫唔寫都得嘅
=-4a+2
=-2(2a-1) / 2(-2a+1)←依步都要寫埋出嚟
3. (2x3+x+1)-(x2+1)←其實你二同三中間果個係乘定係英文字母x?應該唔係乘啦可
=6x+x+1-2x-1
=6x+x-2x+1-1
=(6+1-2)x+0←依步寫唔寫都得嘅
=5x
4. (a3+a2+1)+(a2+2)
=3a+2a+1+2a+2
=3a+2a+2a+1+2
=(3+2+2)a+1+2←依步寫唔寫都得嘅
=7a+3
5. (4-2y+y3)+(y3-y2+2y)
=4-2y+3y+3y-2y+2y
=-2y+3y+3y-2y+2y+4
=(-2+3+3-2+2)y+4←依步寫唔寫都得嘅
=4y+4
=4(y+1)←依步都要寫埋出嚟
6. (m2+n2-mn)-(m2+mn)
=2m+2n-mn-2m-mn
=2m-2m+2n-mn-mn
=(2-2)m+2n+(-1-1)mn←依步寫唔寫都得嘅
=0+2n-2mn
=2(n-mn)←依步都要寫埋出嚟
7. (2a+b)+(b+2c)-(2c-a)
=2a+b+b+2c-2c+a
=2a+a+b+b+2c-2c
=(2+1)a+(1+1)b+(2-2)c←依步寫唔寫都得嘅
=3a+2b+0←依步寫唔寫都得嘅
=3a+2b
8. (2x+y)+(y+3z)-(z-x)
=2x+y+y+3z-z+x
=2x+x+y+y+3z-z
=(2+1)x+(1+1)y+(3-1)z←依步寫唔寫都得嘅
=3x+2y+2z
9. (3xy+y2)-(x2+3xy-y2)
=3xy+2y-2x-3xy+2y
=-2x+2y+2y+3xy-3xy
=-2x+(2+2)y+(3-3)xy←依步寫唔寫都得嘅
=-2x+4y+0
=-2(x-2y) / 2(-x+2y)=2(2y-x)←依步都要寫埋出嚟
其實又無話白唔白痴嘅(咁又唔好咁話自己)，依D數都係折咗括號留意D正負問題有時要轉返(即係正正得正、正負 / 負正得負同埋負負得正果D)唔好折錯跟住調位歸類(即係a還a一堆b還b一堆c還c一堆x還x一堆y還y一堆z還z一堆果D)再化簡返同埋有D要因式分解的就做埋佢，做得多練多D就得架啦希望幫到你啦！！
P.S.寫住「←依步寫唔寫都得嘅」果D只係想比你清楚D明白
2012-07-20 18:56:13 補充：
唔好意思打錯咗個字應該係「拆咗括號」
2012-07-20 19:01:21 補充：
001第一題好似已經錯咗啦喎，最後果個1係負正得負所以拆咗括號就變咗-1(減一)，通常好多人錯都係錯噝拆括號正負果度好正常
2012-07-20 19:15:37 補充：
同埋呢我哋通常有未知數果D都會擺先無論跟住佢(指英文字)果個數都係咁做，所以例如第二題就會-4a+2咁寫最好(無話二寫先唔得只係我哋一向都咁樣寫)，但係好似第九題咁2(-x+2y)，因為括號裡面兩項都有未知數咁就例外，為咗整靚D個答案就調一調咗個位(都係果句唔係話前面果個咁寫唔得)，兩個都係未知數就可以隨意調，除非兩個都係正數就跟返(英文字母表)順序排位，例如最好寫返x+y唔好y+x，如果-x+y就最好寫y-x，死啦好似講得太複雜添唔知你明唔明呢？
2012-07-20 19:24:24 補充：
字數有限問題補充唔到內容唔好意思....
如果第三題二同三中間果個係乘嚟嘅就唔洗理之前果個第三題睇下面果個啦：
3. (2x3+x+1)-(x2+1)
=6+x+1-2x-1
=x-2x+6+1-1
=(1-2)x+6←依步寫唔寫都得嘅
=-x+6
2012-07-20 19:25:16 補充：
請續「意見」...
2012-07-20 19:33:15 補充：
001好似有幾題都唔多正確不過唔緊要嘅都係拆括號拆錯咗的問題
2012-07-26 16:40:34 補充：
哦~好，明哂，咁即係......
3. (2x3+x+1)-(x2+1)
=2x^3+x+1-x^2-1
=2x^3-x^2+x+1-1
=x(2x^2-x+1)
4. (a3+a2+1)+(a2+2)
=a^3+a^2+1+a^2+2
=a^3+a^2+a^2+1+2
=a^3+2a^2+3
5. (4-2y+y3)+(y3-y2+2y)
=4-2y+y^3+y^3-y^2+2y
=y^3+y^3-y^2-2y+2y+4
=2y^3-y^2+4
2012-07-26 16:40:47 補充：
6. (m2+n2-mn)-(m2+mn)
=m^2+n^2-mn-m^2-mn
=m^2-m^2+n^2-mn-mn
=n^2-2mn
=n(n-2m)←寫唔寫都可以
9. (3xy+y2)-(x2+3xy-y2)
=3xy+y^2-x^2-3xy+y^2
=-x^2+y^2+y^2+3xy-3xy
=-x^2+2y^2
=2y^2-x^2或-(x^2-2y^2)←寫唔寫都可以
2012-07-26 16:44:29 補充：
To 回答者：Godfrey
第五條好似有點唔小心，拆咗括號之後-2y同+2y抵消咗所以答案應該係無y項的吧！
