Câu 5: B
Câu 6: D
Câu 7:
a) $\frac{7}{25}$ ; $\frac{-4}{15}$
BCNN(25,15) = 75
TS Phụ: 75 : 25 = 3
75 : 15 = 5
⇒ $\frac{7}{25}$ = $\frac{21}{75}$
$\frac{-4}{15}$ = $\frac{-20}{75}$
b)$\frac{3}{4}$ ; $\frac{1}{9}$ ; $\frac{-5}{8}$
BCNN(4, 9, 8) = 72
TS Phụ: 72 : 4 = 18
72 : 9 = 8
72 : 8 = 9
⇒ $\frac{3}{4}$ = $\frac{54}{72}$
$\frac{1}{9}$ = $\frac{8}{72}$
$\frac{-5}{8}$ = $\frac{-45}{72}$
c) $\frac{54}{-90}$ ; $\frac{-180}{288}$ ; $\frac{60}{-135}$
Rút gọn về mẫu dương: $\frac{-3}{5}$ ; $\frac{-5}{8}$ ; $\frac{-4}{9}$
BCNN(5, 8, 9) = 360
TS Phụ: 360 : 5 = 72
360 : 8 = 45
360 : 9 = 40
⇒ $\frac{-3}{5}$ = $\frac{-216}{360}$
$\frac{-5}{8}$ = $\frac{-225}{360}$
$\frac{-4}{9}$ = $\frac{-160}{360}$
Câu 8:
$-4 = $$\frac{-36}{9}$
$\frac{2}{3}$$ = $$\frac{6}{9}$
$0 = $$\frac{0}{9}$
$\frac{85}{153}$$ = $$\frac{5}{9}$
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