1. The problem statement, all variables and given/known data First I'd like to state the meaning of my notations x = (x0,x1,x2...xn) y = (y0,y1,y2...yn) |x| = absolute value of x ||x|| = Normal of x <x,y> = Inner Product of x and y I have to prove the following |<x1,y1> - <x2,y2>| ≤ ||x1 - x2||*||y1|| + ||x2||*||y1-y2|| 2. Relevant equations Applicable Axioms of Normals and Inner Products ||x|| = √(<x,x>) <x + z,y> = <x,y> + <z,y> 3. The attempt at a solution I tried expanding the right hand side as such: ||x1 - x2|| = √(<x1-x2,x1-x2>) = √(<x1,x1> + 2*<x1,-x2> + <-x2,-x2>) ||x2|| = √(<x2,x2>) I did similarly for the y values, and I'm not seeing anything that pops out to me as a solution to this proof, nothing seems to cancel, and no axioms seem to make this work in a general sense. I guess what I need...is a HINT.