Bài 7: Phép trừ hai số nguyên

vì nó = 1

=1 :)

Vì - 1 =1 x (-1)

=> - - 1 = (-1)x (-1) = 1

a) \(\dfrac{2}{3}+20\%\cdot\dfrac{10}{7}=\dfrac{2}{3}+\dfrac{1}{5}\cdot\dfrac{10}{7}=\dfrac{2}{3}+\dfrac{2}{7}=\dfrac{20}{21}\)

b) \(\dfrac{3}{4}+1\dfrac{4}{5}:\dfrac{3}{2}-1=\dfrac{3}{4}+\dfrac{9}{5}:\dfrac{3}{2}-1=\dfrac{3}{4}+\dfrac{6}{5}-1=\dfrac{39}{20}-1=\dfrac{19}{20}\)

c,d tự làm

a) \(0,75+\dfrac{-1}{3}-\dfrac{5}{18}=\dfrac{3}{4}+\dfrac{-1}{3}-\dfrac{5}{18}=\dfrac{5}{12}-\dfrac{5}{18}=\dfrac{5}{36}\)

b) \(7\dfrac{3}{5}-\left(2\dfrac{5}{7}+5\dfrac{3}{5}\right)=\dfrac{38}{5}-\left(\dfrac{19}{7}+\dfrac{28}{5}\right)=\dfrac{38}{5}-\dfrac{19}{7}+\dfrac{28}{5}=\left(\dfrac{38}{5}-\dfrac{28}{5}\right)+\dfrac{19}{7}=2+\dfrac{19}{7}=\dfrac{33}{7}\)

c) \(\dfrac{4}{15}\cdot\dfrac{1}{3}\cdot\dfrac{15}{20}=\dfrac{4}{15}\cdot\dfrac{1}{3}\cdot\dfrac{3}{4}=\dfrac{4}{45}\cdot\dfrac{3}{4}=\dfrac{12}{180}=\dfrac{1}{15}\)

d) \(\dfrac{-1}{9}\cdot\dfrac{15}{22}:\dfrac{-25}{9}=\dfrac{-5}{66}:\dfrac{-25}{9}=\dfrac{-5}{66}\cdot\dfrac{-9}{25}=\dfrac{3}{110}\)

=-5

-5

-5

số âm hoặc số dương

số âm

số dương

=87

=20-46-25+46

=-26-25+46

=-51+46=-5

a: 1/2-1/3=1/6

b: 1/5-1/6=1/30

c: 1/3-1/4=1/12

d: 1/7-1/8=1/56

\(\dfrac{1}{2}-\dfrac{1}{3}=\dfrac{3}{6}-\dfrac{2}{6}=\dfrac{1}{6}\)

\(\dfrac{1}{5}-\dfrac{1}{6}=\dfrac{6}{30}-\dfrac{5}{30}=\dfrac{1}{30}\)

\(\dfrac{1}{3}-\dfrac{1}{4}=\dfrac{4}{12}-\dfrac{3}{12}=\dfrac{1}{12}\)

\(\dfrac{1}{7}-\dfrac{1}{8}=\dfrac{8}{56}-\dfrac{7}{56}=\dfrac{1}{56}\)

a. 1/6 b.1/30 c. 1/12 d. 1/56  

Bài 4: Tìm x

a. \(\left(2x-5\right)+17=6\)

\(2x-5=6-17\)

\(2x-5=-11\)

\(2x=-11+5\)

\(2x=-6\)

\(x=-3\)

b.\(10-2\left(4-3x\right)=-4\)

\(-2\left(4-3x\right)=-4-10\)

\(-8+6x=-14\)

\(6x=-6\)

\(x=-1\)

c. \(-12+3\left(-x+7\right)=-18\)

\(3\left(-x+7\right)=-18+12\)

\(-3x+21=-6\)

\(-3x=-27\)

\(x=9\)

d.\(24:\left(3x-2\right)=-3\)

\(24:\left(-3\right)=3x-2\)

\(-8=3x-2\)

\(-6=3x\)

\(x=-2\)

- 84

- 25

= -84
= -25

12 - 96 = -84
72 - 97 =-25

15 độ

3 độ