# Writing a proof the correct way

1. Sep 12, 2012

### grjmmr

1. The problem statement, all variables and given/known data

k:= {s+t√2:s,t$\in$Q}, if x1 and x2 $\in$ K, prove x1 +x2$\in$K

2. Relevant equations

3. The attempt at a solution
My thought is that x1 and x2 $\in$K$\in$Q$\subseteq$R thus by algerbraic properties X1+x2 =X3 which also $\in$ K. this seems just a little too easy, am i correct in my line of thinking?

2. Sep 12, 2012

### LCKurtz

You need more detail. What you have to show is that $x_1+x_2$ can be written in the form $s+t\sqrt 2$ where $s,t\in Q$, where I presume $Q$ is the rationals, although you never specifically said that.