幫我做d數學題!急....20點

1. -3y²-9y-5-5y+6y²-4+7y²-8y-11
=10y²-22y+12
=2(5y²-11y+6)

2012-08-25 20:15:06 補充：
2. -12+8x-x²+8-14x-5x²-2+3x+4x²
= -6 -3x-2x²

2012-08-25 20:16:48 補充：
3. 16x-4-7x-20+10x-7
= 19x-11

2012-08-25 20:21:20 補充：
4. -2x+4y+7+1-3y+7y+2
= -2x+8y+9

5. 3a-7a+6b+4a-11b-4b
= 13b

6. 14a-23b-(16a-7-18a+7b-11a-9b-7)
= 14a-23b-(-13a-2b-14)
= 14a-23b+13a+2b+14
= 27a-21b+14

2012-08-25 20:28:17 補充：
1.
2y-0.25=0.75(4y-3)
(8y-1)/4 = 3(4y-3)/4
8y-1=12y-9
8=4y
y=2

2.
0.3(2a-5)-0.04a=0.66
0.6a-1.5-0.04a=0.66
0.56a=2.16
a=3.857

3.
2.8-6(0.3-1.2x)=6x
2.8-1.8+7.2x=6x
1=-1.2x
x= -0.834

4.
y+2/3 + 7-2y/5 =0
3y/5 = 23/3
y = 115/9

1)
-(3y² + 9y - 5) - (5y - 6y² + 4) + (7y² - 8y - 11)
= -3y² - 9y + 5 - 5y + 6y² - 4 + 7y² - 8y - 11
= (-3y² + 6y² + 7y²) + (-9y - 5y- 8y) + (5 - 4 - 11)
= 10y² - 22y -10
= 2(5y² - 11y - 5)


2)
-(12 - 8x + x²) + (8 - 14x - 5x²) + (-2 + 3x + 4x²)
= -12 + 8x - x² + 8 - 14x - 5x² - 2 + 3x + 4x²
= (-x² - 5x² + 4x²) + (8x - 14x + 3x) + (-12 + 8 - 2)
= -2x² - 3x - 6


3)
16x - (4 + 7x) - [20 - (10x - 7)]
= 16x - 4 - 7x - [20 - 10x + 7]
= 16x - 4 - 7x - 20 + 10x - 7
= (16x - 7x + 10x) + (-4 - 20 - 7)
= 19x - 31


4)
-(2x - 4y - 7) + [1 - (3x - 7y - 2)]
= -2x + 4y + 7 + [1 - 3x + 7y + 2]
= -2x + 4y + 7 + 1 - 3x + 7y + 2
= (-2x - 3x) + (4y + 7y) + (7 + 1 + 2)
= -5x + 11y + 10


5)
3a - [7a - 6b - (4a - 11b)] - 4b
= 3a - [7a - 6b - 4a + 11b] - 4b
= 3a - 7a + 6b + 4a - 11b - 4b
= (3a - 7a + 4a) + (6b - 11b - 4b)
= -9b


6)
(14a - 23b) - [(16a - 7) - (18a - 7b) + (-11a - 9b - 7)]
= 14a - 23b - [16a - 7 - 18a + 7b - 11a - 9b - 7]
= 14a - 23b - 16a + 7 + 18a - 7b + 11a + 9b + 7
= (14a - 16a + 18a + 11a) + (-23b - 7b + 9b) + (7 + 7)
= 27a - 21b + 14


1)
2y - 0.25 = 0.75(4y - 3)
2y - 0.25 = 3y - 2.25
-y = -2
y = 2


2)
0.3(2a - 5) - 0.04a = 0.66
0.6a -1.5 - 0.04a = 0.66
0.56a = 2.16
a = 2.16/0.56
a = 27/7


3)
2.8 - 6(0.3 - 1.2x) = 6x
2.8 - 1.8 + 7.2x = 6x
1.2x = -1
x = -1/1.2
x = -5/6


4)
(y + 2)/3 + (7 - 2y)/5 =0
(y + 2)/3 = -(7 - 2y)/5
5(y + 2) = -3(7 - 2y)
5y + 10 = -21 + 6y
y = 31