1. tính hợp lí
a. A=\(\dfrac{1}{3}\)+\(\dfrac{-3}{4}\)+\(\dfrac{3}{5}\)+\(\dfrac{1}{57}\)+\(\dfrac{-1}{36}\)+\(\dfrac{1}{15}\)+\(\dfrac{-2}{9}\)
b. B=\(\dfrac{1}{2}\)+\(\dfrac{-1}{5}\)+\(\dfrac{-5}{7}\)+\(\dfrac{1}{6}\)+\(\dfrac{-3}{35}\)+\(\dfrac{1}{3}\)+\(\dfrac{1}{41}\)
c. C=\(\dfrac{-1}{2}\)+\(\dfrac{3}{5}\)+\(\dfrac{-1}{9}\)+\(\dfrac{1}{107}\)+\(\dfrac{-7}{18}\)+\(\dfrac{4}{35}\)+\(\dfrac{2}{7}\)