Originally Posted by

**ruprotein** Does anyone know how to write a FORMAL PROOF for (For all real numbers x)(-(-x)=x)

using the definition (For all real numbers x)(-x = 0-x)

So i need to obviously use the axioms of arithmitec etc... any1 can help me do it? it should take about 20 steps not much less but shouldntbe greater than 20

http://www.math.rutgers.edu/~sussmann/papers/hmw10.pdf is where the axiom rules can be foudn ont he last part of the page

Code:

def: for all real x: -x=0-x
1. -x=0-x ..(def)
2. x+(-x)=0 ..(1 and Sub2)
3. (-x)+x=0 ..(2 and Add2)
4. x=0-(-x) ..(3 and Sub2)
5. x=-(-x) ..(4 and def)

RonL