Đáp án:
a) $ \frac{81}{216},\frac{40}{216}$
b) $ \frac{1}{15}, \frac{-90}{15}$
c) $\frac{77}{126}, \frac{102}{126}$
d)$\frac{-15}{63}, \frac{28}{63}$
Giải thích các bước giải:
$a) 8=2^3\\
27=3^3\\
BCNN(8,27)=2^3.3^3=216\\
\frac{3}{8}=\frac{3.27}{8.27}=\frac{81}{216}\\
\frac{5}{27}=\frac{5.8}{27.8}=\frac{40}{216}\\
b) MSC: 15
\frac{1}{15}\\
-6=\frac{(-6).15}{15}=\frac{-90}{15}\\
c)
18=3^2.2\\
21=3.7\\
BCNN(18,21)=2.3^2.7=126\\
\frac{11}{18}=\frac{11.7}{18.7}=\frac{77}{126}\\
\frac{17}{21}=\frac{17.6}{21.6}=\frac{102}{126}\\
d)
21=3.7\\
9=3^2\\
BCNN(21,9)=3^2.7=63\\
\frac{-5}{21}=\frac{(-5).3}{21.3}=\frac{-15}{63}\\
\frac{4}{9}=\frac{4.7}{9.7}=\frac{28}{63}$
