### Using the solution of equation

How can I use after solve(eq) the result? For example, the result for this simple linear system

```
[x + 2*y + 4*z - 1]
[ x + 4*z - 5]
[ 3*x + 6*z - 6]
```

is

```
[[x == -1, y == -2, z == (3/2)]]
```

How can I use x,y,z in an expression, say x^2+y^2+z^2 ?