Bài 1 :
a, $\frac{-1}{39}$ + $\frac{-1}{52}$= $\frac{-7}{156}$
b, $\frac{-6}{9}$+ $\frac{-12}{16}$= $\frac{-2}{3}$+ $\frac{3}{4}$ = $\frac{-17}{12}$
c, $\frac{-2}{5}$- $\frac{-3}{11}$= $\frac{-7}{55}$
d, $\frac{-5}{12}$ + 0,75= $\frac{1}{3}$
e, $\frac{5}{7}$ . 12$\frac{1}{2}$ -$\frac{5}{7}$ . 5$\frac{1}{2}$ = $\frac{5}{7}$.(6- $\frac{5}{2}$) = $\frac{5}{7}$ - $\frac{7}{2}$ =$\frac{-39}{14}$
Bài 2 :
a, A = 2/3 + 3/4 (-4/9)
A= 17/12 . (-4/9)
A= -17/27
b, B= -3/4 . 5 3/13 - 0,75 - 36/13
B = -3/4 . 15/13 - 3/4. 36/13
B = (36/13 . -3/4) - ( 15/13 . 3/4)
B = -27/13 - 45/92
c, C = ( 3/4 - 0,2) . (0,2-4/5)
C= (3/4 - 1/5) . ( 1/5 - 4/5)
C= 11/20 . (-3/5)
C = -33/100
II. Dạng 2 tìm x
Bài 1
a, x + 13/10 = -2/15
x = -2/15 - 13/10
x= -12/30
b, x + 5/6 = 2/5 - (-2/3)
x + 5/6 = 16/15
x = 16/15 - 5/6
x = 7/30
c, 13/20 + (3/5 - x) = 5/8
13/20 + x = 5/8 + 3/5
13/20 + x = 49/40
x = 49/40 - 13/20
x = 23/40
Bài 2 :
a, x : 3/8 = -131 /33
x = -131/33 . 3/8
x = -131/88
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