how do you solve lineear equations with 3 unknowns on a casio fx83-ES?

Answer 1

steps to follow
1) press mode untill you see eqn.
2) press the number displaying corresponding to eqn. mode.
3) you will see 2 and 3
4) press 3
5) then feed the co-efficents of x as a1
6) press equal
7) then feed the co-efficent 0f y as b1
8) press equal
similarly feed the other co-efficients.
9)then press equal yu will get value of x
10)then press equal yu will get value of y
11)then press equal yu will get value of z

Answer 2

If the unknowns are a,b,c, then then manipulate two of the equations to eliminate one of the variables, say c.
Now use two different equations to eliminate c again.

You now have two equations in a and b which you can solve by elimination or substitution.