[latex]a)quad |+5|+|-9|-|-3|+|+8|=\ \ =(5)+(9)-(3)+(8) = \ \ = 5+9-3+8 = 14+5 = 19[/latex] [latex]b)quad 1-2+3-4+5-6+...+101-102= \ \ = -1-1-1- underset{ ext{de 56 ori}}{underbrace{...}} - 1 = -56[/latex]