Which statement best describes how to determine whether fx=x3+5x+1 is an even function? Determine whether -x3+5x+1 is equivalent to x3+5x+1. Determine whether -x3+5-x+1 is equivalent to x3+5x+1. Determine whether -x3+5x+1 is equivalent to -x3+5x+1 Determine whether -x3+5-x+1 is equivalent to -x3+5x+1