a: =-1/21-3/21=-4/21
b: =-20/36-3/36=-23/36
c: =12/3-2/3=10/3
e: =10/7+3/14-4=20/14+3/14-56/14=-33/14
`(-1)/21 + (-1)/7`
`=(-1)/21 - 1/7`
`=(-1)/21 - 3/21`
`=(-4)/21`
__________________
`7,4 - (-7)/5`
`= 7,4 + 7/5`
`= 37/5 + 7/5`
`=44/5`
__________________
`4-2/3`
`=12/3-2/3`
`=(12-2)/3`
`=10/3`
_________________________
`(10/7-4)+3/14`
`=(10/7-28/7)+3/14`
`=(-18)/7+3/14`
`=(-36)/14+3/14`
`=(-36+3)/14`
`=-33/14`
_________________________
`2/3 -(-1)/4 + 1/15 + 1/20`
`= 2/3 + 1/4 + 1/15 + 1/20`
`=(2/3+1/15)+(1/4+1/20)`
`= (10/15+1/15)+(5/20+1/20)`
`=11/15 + 6/20`
`= 11/15 + 3/10`
`= 22/30 + 9/30`
`=31/30`
_____________________________
`A = ( 3 - 1/4+2/3)-(5+1/3-6/5)-(6-7/4+3/2)`
`A = 3 - 1/4 + 2/3 - 5 - 1/3 + 6/5 - 6 + 7/4 - 3/2`
`A = ( 3 - 5 - 6) + (-1/4 + 7/4) + ( 2/3 - 1/3) + ( 6/5 - 3/2)`
`A = -8 + 6/4 + 1/3 + (-3)/10`
`A = -8 + 3/2 + 1/3 + (-3)/10`
`A= (-240)/30 + 45/30 + 10/30 + (-9)/30`
`A = (-240 + 45 + 10 - 9)/30`
`A= (-194)/30`
`A= (-97)/15`
Bài 1: Thực hiện phapes tính:
a, $\dfrac{-1}{21}$ + $\dfrac{-1}{7}$
= $\dfrac{-1}{21}$ + $\dfrac{-1.3}{7.3}$
= $\dfrac{-1}{21}$ + $\dfrac{-3}{21}$
= $\dfrac{-1+-3}{21}$
= $\dfrac{-4}{21}$
b, $\dfrac{-5}{9}$ - $\dfrac{1}{12}$
= $\dfrac{-5.12}{9.12}$ - $\dfrac{1.9}{12.9}$
= $\dfrac{-60}{108}$ - $\dfrac{9}{108}$
= $\dfrac{-60-9}{108}$
= $\dfrac{-69}{108}$
= $\dfrac{-23}{36}$
b, 7,4 - (-$\dfrac{7}{5}$)
= $\dfrac{37}{5}$ - (-$\dfrac{7}{5}$)
= $\dfrac{37-(-7)}{5}$
= $\dfrac{44}{5}$
c, 4 - $\dfrac{2}{3}$
= $\dfrac{4}{1}$ - $\dfrac{2}{3}$
= $\dfrac{4.3}{1.3}$ - $\dfrac{2.1}{3.1}$
= $\dfrac{12}{3}$ - $\dfrac{3}{3}$
= $\dfrac{12-3}{3}$
= $\dfrac{9}{3}$
= 3
e, ($\dfrac{10}{7}$ - 4) + $\dfrac{3}{14}$
= ($\dfrac{10}{7}$ - $\dfrac{4}{1}$) + $\dfrac{3}{14}$
= ($\dfrac{10.1}{7.1}$ - $\dfrac{4.7}{1.7}$) + $\dfrac{3}{14}$
= ($\dfrac{10}{7}$ - $\dfrac{28}{7}$) + $\dfrac{3}{14}$
= ($\dfrac{10-28}{7}$) + $\dfrac{3}{14}$
= $\dfrac{-18}{7}$ + $\dfrac{3}{14}$
= $\dfrac{-18.2}{7.2}$ + $\dfrac{3}{14}$
= $\dfrac{-36}{14}$ + $\dfrac{3}{14}$
= $\dfrac{-36+3}{14}$
= $\dfrac{-33}{14}$
d, $\dfrac{2}{3}$ - $\dfrac{-1}{4}$ + $\dfrac{1}{15}$ + $\dfrac{1}{20}$
= $\dfrac{2}{3}$ + $\dfrac{1}{4}$ + $\dfrac{1}{15}$ + $\dfrac{1}{20}$
= $\dfrac{2.4}{3.4}$ + $\dfrac{1.3}{4.3}$ + $\dfrac{1}{15}$ + $\dfrac{1}{20}$
= $\dfrac{8}{12}$ + $\dfrac{3}{12}$ + $\dfrac{1}{15}$ + $\dfrac{1}{20}$
= $\dfrac{8+3}{12}$ + $\dfrac{1}{15}$ + $\dfrac{1}{20}$
= $\dfrac{11}{12}$ + $\dfrac{1}{15}$ + $\dfrac{1}{20}$
= $\dfrac{11.5}{12.5}$ + $\dfrac{1.4}{15.4}$ + $\dfrac{1}{20}$
= $\dfrac{55}{60}$ + $\dfrac{4}{60}$ + $\dfrac{1}{20}$
= $\dfrac{55+4}{60}$ + $\dfrac{1}{20}$
= $\dfrac{59}{60}$ + $\dfrac{1}{20}$
= $\dfrac{59}{60}$ + $\dfrac{1.3}{20.3}$
= $\dfrac{59}{60}$ + $\dfrac{3}{60}$
= $\dfrac{59+3}{60}$
= $\dfrac{62}{60}$
= $\dfrac{31}{30}$
