方程maths

最好用聯立去做，易明，無咁煩
5)設大數為x小數為y
x-y=26....(1)
x-2y=2.....(2)

x=26+y....(3)
把3代入2
(26+y)-2y=2
y=24
把y=24代入(1)
x-(24)=26
x=50
大數為50

6)x=2y.....(1)
(3+x)+(3+y)=42.....(2)
把(1)代入(2)
3+(2y)+3+y=42
y=6
把y=6代入(1)
x=2(6)
x=12

7) 2a-1/3a=10
a=6

8)x-y=5....(1)
(4+x)+(4+y)=33....(2)

x=5+y....(3)
把(3)代入(2)

4+(5+y)+4+y=33
y=6
把y=6代入(1)
x-(6)=5
x=11
X現年11歲

9)設較小數為x，較大數為y

3x=2y+6....(1)
x+y=17....(2)
從(2)...
x=17-y....(3)
把(3)代入(1)]
3(17-y)=2y+16
5y=45
y=9
把y=9代入(2)
x+(9)=17
y =8

希望以上計ge數無錯

2006-12-31 13:56:16 補充：
第9條最後係x=8唔係y=8(手快打錯)

Q.5 = 40
Q.6 = 24
Q.7 = 6
Q.8 = 10
Q.9 = 9

Q5
設大數是X,小數是Y
X - Y = 26
X - 26 = Y
3/4X - 2Y = 2 代入
3/4X - 2( X - 26 ) = 2
3/4X - 2X + 52 = 2
- 5/4X = - 50
X = 40

Q6
X = 2Y
X/2 = Y
X + 3 + Y + 3 = 42
X + Y +6 = 42
X + Y = 36 代入
X + X/2 = 36
1.5X = 36
X = 24

Q7
2a - 1/3a = 10
5/3a = 10
a = 6

Q8
X + 5 = Y
X + 4 + Y + 4 = 33
X + Y + 8 = 33
X + Y = 25 代入
X + X + 5 = 25
2X + 5 = 25
2X = 20
X = 10

Q9
設大數是X,小數是Y
3Y - 2X = 6
X + Y = 17
X = 17 - Y
3Y - 2( 17 - Y ) = 6
3Y - 34 + 2Y = 6
5Y - 34 = 6
5Y = 40
Y = 8
X + 8 = 17
X = 9

5.設大數為x, 小數為y,
x - y = 26 .....(1)
3x/4 - 2y = 2 .....(2)

From (1),
x - y = 26
y = x - 26 ...(3)

sub (3) into (2)
3x/4 - 2(x - 26) = 2
3x - 8(x - 26) = 8
3x - 8x + 208 = 8
-5x = -200
x = 40
大數為40

6. 設XX的歲數為a, YY的歲數為b,
a = 2b...(1)
a + 3 + b +3 = 42...(2)

sub (1) into (2),
2b + 3 + b +3 = 42
3b = 36
b = 12...(3)

sub (3) into (1),
a = 24
XX現年24歲

7. 2a - a/3 = 10
6a - a = 30
5a = 30
a = 6

8. 設XX的歲數為a, YY的歲數為b,
a - b = 5...(1)
a + 4 + b + 4 = 33...(2)

Form (1)
b = a - 5...(3)

Sub (3) into (2)
a + 4 + a - 5 + 4 = 33
2a = 30
a = 15
XX現年15歲

9. 設較大的數為x, 較小的數為y,
3y - 2x = 6...(1)
x + y = 17...(2)

From (2),
x + y = 17
x = 17 - y...(3)

Sub (3) into (1)
3y - 2(17 - y) = 6
3y - 34 + 2y = 6
5y = 40
y = 8...(4)

Sub (4) into (3),
x = 17 - 8
x = 9
較大的數為9
較小的數為8

2006-12-31 13:49:43 補充：
上面o個個...第9條y = 9 之後...你sub 左...跟住y 又 = 8?