解一元一次方程

圖片參考：http://img220.imageshack.us/img220/1605/sol18.png

As a few helpers have answered before
1)
a=-1.9
2)
y=5/7=0.714,cor to 3 sig fig



2010-11-17 13:10:58 補充：
http://img220.imageshack.us/img220/1605/sol18.png

1)
2a+3/4 - a+4/3 =a+1
(2a+3)/4-(a+4)/3 = a+1
3(2a+3)-4(a+4) = 12(a+1)
6a+9-4a-16 = 12a+12
9-16+12 = 12a-6a+4a
5 = 10a
a = 5/10
a = 1/2


2)
2y-1 + 1+y/4 =1 - 1-y/2
(2y-1) + (1+y)/4 = 1- (1-y)/2
4(2y-1)+(1+y) = 4*1 - 2(1-y)
8y-4+1+y = 4-2+2y
8y+y-2y = 4-2+4-1
7y = 5
y = 5/7


3)
5/6 (x-2)+1.3=7x/10 +0.5x
5*5(x-2)+30*1.3 = 3*7x+30*0.5x
25x-50+39 = 21x+15x
25x-21x-15x=50-39
-11x = 11
x = 11/(-11)
x = -1


解下列以y為未知數的文字方程。

34)
y/z +A=3- 2y/5z
5y + 5Az = 5z*3 - 2y
5y+2y = 15z-5Az
7y = 15z(3-A)
y = [15z(3-A)] / 7



2010-11-17 20:54:17 補充：
girl

2a + 3/4 - a + 4/3 = a + 1
2a - a - a = 1 - 3/4 - 3/4
0 = -1/2 ( Contradiction for they are unequal )

As a few helpers have answered before, I only concentrate on your Question 1 which has no solution at all. Why?

2a + 3/4 - a + 4/3 = a + 1
2a - a - a = 1 - 3/4 - 3/4
0 = -1/2 ( Contradiction for they are unequal )
Hence, the equation has no solution.
It has no solution because the L.H.S can never be equal to R.H.S. for all possible values of x.

第一題都計唔到-.-