數學代數問題(10)

1.)5[(11 3y)/2] 3y=17
(55 15y)/2 3y=17
55 15y 6y=34
21y= -21
y= -1

2) 5[(9+3y)/2] 4y=11
(45+15y)/2 4y=11
45+15y 8y=22
23y= -23
y= -1

3) 5/6 [(2-1/3y)2] 2y=-1
5/6[( -1/3y)2] 2y= -1
5/6[-2/3y] 2y= -1
-10/18y 2y= -1
-5/9y 2y= -1
13/9y= -1
13= -9y
y= -13/9

2008-03-31 14:31:27 補充：
我第三題個唔知做乜野唔見曬d加號......
3) 5/6 [(2-1/3y)2]+2y=-1
5/6[( -1/3y)2]+2y= -1
5/6[-2/3y]+2y= -1
-10/18y+2y= -1
-5/9y+2y= -1
13/9y= -1
13= -9y
y= -13/9
應該係學得呢一條咁先啱.....

5[(11+3y)/2]+3y=17
5[(11+3y)/2]=17-3y
(55+15y)/2=17-3y
55+15y=34-6y
15y+6y=34-55
21y=-21
y=-1


5[(9+3y)/2]+4y=11
5[(9+3y)/2]=11-4y
(45+15y)/2=11-4y
45+15y=22-8y
15y+8y=22-45
23y=-23
y=-1


5/6 [(2-1/3y)2]+2y=-1
5/6 [(2-1/3y)2]=-1-2y
5[(2-1/3y)2]=-6-12y
5(2-1/3y)=-3-6y
10-5/3y=-3-6y
6-5/3y=-3-10
y(18-5)/3=-13
13y=-39
y=-3

1)
5(11/2+3y/2)+3y=17
55/2+15y/2+3y =17
21y/2 =17-55/2
y =-1
2)
5(9/2+3y/2)+4y=11
45/2+15y/2+4y =11
23y/2 =11-45/2
y =-1

3)
5/6 (4-2/3y) +2y=-1
20/6 - 5/9y+ 2y=-1
- 5/9y+ 2y=-13/4
- 5+ 18y^2=-117y/4
0=18y^2 + 117y/4 -5
y=0.156 or -1.78

2008-04-03 22:47:37 補充：
3. 用quadratic equation:
x=[-b +- Square root(b^2-4ac)]/2a