Question 1065496
Prove: |x+y| ≤ |x|+|y|
<pre><b<font size=4>
We use the fact that a &#8804; |a| for all real numbers a,
that the square root function is an increasing function, 
and that {{{abs(a)=sqrt(a^2)}}}

{{{abs(x+y)=sqrt((x+y)^2)=sqrt(x^2+2xy+y^2)<=sqrt(abs(x)^2+2abs(x)abs(y)+abs(y)^2)=sqrt((abs(x)+abs(y))^2)=abs(x)+abs(y)}}}  

Edwin</pre></b></font>