Question

3.

Answer 1

Giải:

a) \(\dfrac{3}{5}+\dfrac{-5}{9}=\dfrac{27}{45}+\dfrac{-25}{45}=\dfrac{27+\left(-25\right)}{45}=\dfrac{2}{45}\) 

b) \(\dfrac{4}{13}+\dfrac{-12}{39}=\dfrac{4}{13}+\dfrac{-4}{13}=\dfrac{4+\left(-4\right)}{13}=\dfrac{0}{13}=0\) 

c) \(\dfrac{8}{40}+\dfrac{-36}{45}=\dfrac{1}{5}+\dfrac{-4}{5}=\dfrac{1+\left(-4\right)}{5}=\dfrac{-3}{5}\) 

d) \(\dfrac{7}{21}+\dfrac{-9}{39}=\dfrac{1}{3}+\dfrac{-3}{13}=\dfrac{13}{39}+\dfrac{-9}{39}=\dfrac{13+\left(-9\right)}{39}=\dfrac{4}{39}\)

Answer 2

a,3/5+-5/9=27/45+-25/45=2/45

b,4/13+-12/39=12/39+-12/39=0

Answer 3

c,8/40+-36/45=1/5+-4/5=-3/5

d,7/21+-9/39=1/7+-3/13=13/91+-21/91=-8/91