Chapter P - Prerequisites: Fundamental Concepts of Algebra - Exercise Set P.1 - Page 20: 154

false; $-x-x=-2x$

Start by checking if there are two identities for the equations, and then simplify the expression. $-x-x=-x+(-x)=0$ $-x-x=-x-x=0$ $-x-x=-x-x$ $-x-x=-2x$ The first two expressions are identical, while the last one is different, making the statement false.