# How do i solve the system of equation

1. Jun 22, 2010

### lorik

1. The problem statement, all variables and given/known data
I need to find a,b,c from
a+b-c=0.1
2a-b-c=0
a+b+c=0.3

2. Relevant equations

3. The attempt at a solution

The furthest Ive gone is
a+b+c=0.1
3a=0.3=>0.1

2. Jun 22, 2010

### thebigstar25

im not sure what you have done?
you can start by subtracting the first equation from third equation, then you will have the value of c
after that you can use this value in the second equation to get either a in terms of b or b in terms of a, after that you can easily substitute again in the first or third equation to get your answer..

3. Jun 22, 2010

### Staff: Mentor

You lost your variable! 3a = .3 ==> a = .1
Now substitute for a in two other equations to get two equations in b and c, which you can solve for those variables.

4. Jun 22, 2010

### HallsofIvy

Staff Emeritus
What you did the first time was add the second and third equations, eliminating both b and c at the same time to get a= .1.

Now, you can, as Mark44 suggests, set a= .1 in those three equations reducing to two equations for b and c. (Only two equations because a= .1 makes the second and third equations, that you used to get a, the same.)

Or you can do as Thebigstar25 suggests- subtract the first equation from the third equation. That eliminates both a and b at the same time, allowing you to solve for c.

Once you have found a and c, put those values into any of the three equations and solve for b.

5. Jun 22, 2010

### lorik

Ok thanks for the fast reply because it really helped !

6. Jun 22, 2010

### wwshr87

I do not know if you have learned about Cramer's Rule, but you might want to look into this, it will make this problem very simple to solve.

Last edited: Jun 22, 2010