Question

Tính nhanh giá trị các biểu thức sau:

\(\dfrac{-7}{21}\)+(1+\(\dfrac{1}{3}\))             \(\dfrac{2}{15}\)+(\(\dfrac{5}{9}\)+\(\dfrac{-6}{9}\))             (\(\dfrac{-1}{5}\)+\(\dfrac{3}{12}\)) + \(\dfrac{-3}{4}\)

lm đi mik tích cho hứa

Answer 1

a: =-1/3+1/3+1=1

b: =2/15+5/9-6/9

=2/15-1/9

=6/45-5/45=1/45

c: =-1/5+1/4-3/4

=-1/5-1/2

=-7/10

Answer 2

-7/21 + ( 1 + 1/3 )

= -1/3 + 1 + 1/3

= -1/3 + 1/3 + 1

= 0 + 1

= 1

2/15 + ( 5/9 + -6/9 ) 

= 2/15 + -1/9

= 6/45 + -5/45

= 1/45

( -1/5 + 3/12 ) + -3/4

= -1/5 + 1/4 + -3/4

= 1/4 + -3/4 + -1/5

= -1/2 + -1/5

= -5/10 + -2/10

= -7/10

Answer 3

\(\dfrac{-7}{21}+\left(1+\dfrac{1}{3}\right)=\dfrac{-1}{3}+1+\dfrac{1}{3}=\left(\dfrac{-1}{3}+\dfrac{1}{3}\right)+1=0+1=1\)

\(\dfrac{2}{15}+\left(\dfrac{5}{9}+\dfrac{-6}{9}\right)=\dfrac{2}{15}+\dfrac{-1}{9}=\dfrac{6}{45}+\dfrac{-5}{45}=\dfrac{1}{45}\)

\(\left(\dfrac{-1}{5}+\dfrac{3}{12}\right)+\dfrac{-3}{4}=\left(\dfrac{-12}{60}+\dfrac{15}{60}\right)+\dfrac{-3}{4}=\dfrac{3}{60}+\dfrac{-3}{4}=\dfrac{3}{60}+\dfrac{-45}{60}=\dfrac{-42}{60}=\dfrac{-7}{10}\)