Find A, B, & C

David Cohen Textbook Questions.
Enjoy.

 

a+b=7
-2b+c=-9
9a-2c=29
_________________

a+b=7
a=7-b.....1)

9a-2c=29
a=(29+2c)/9.....2)

from 1) and 2) we have

7-b=(29+2c)/9
b= 7-(29+2c)/9
b = 34/9 - (2 c)/9....3)


-2b+c=-9
9+c=2b
b=(9+c)/2..........4)

from 3) and 4) we have

34/9 - (2 c)/9=(9+c)/2
-(13 c)/18 - 13/18 = 0
c=-1

go to

b=(9+c)/2..........4), substitute c
b=(9-1)/2
b=4

go to

a=7-b.....1), substitute b
a=7-4
a=3

solutions:
a = 3, b = 4, c = -1

 

I have trouble solving three equations, three unknowns. Ever did four equations, four unknowns? David Cohen has a few in his textbook.