Đáp án:
a.$\dfrac{21}{13}=\dfrac{42}{26}=\dfrac{-42}{-26}$
b.$\dfrac{12}{-25}=\dfrac{24}{-50}=\dfrac{-24}{50}$
c.$\dfrac{18}{-48}=\dfrac{36}{-96}=\dfrac{3}{-8}$
d.Ta có:
$\dfrac{-42}{-24}=\dfrac{-42\cdot (-1)}{-24\cdot (-1)}=\dfrac{42}{24}$
$\dfrac{-42}{-24}=\dfrac{-42:(-2)}{-24:(-2)}=\dfrac{21}{12}$
Giải thích các bước giải:
a.Ta có:
$\dfrac{21}{13}=\dfrac{21\cdot 2}{13\cdot 2}=\dfrac{42}{26}$
$\dfrac{21}{13}=\dfrac{21:(-1)}{13:(-1)}=\dfrac{-42}{-26}$
b.Ta có:
$\dfrac{12}{-25}=\dfrac{12\cdot 2}{-25\cdot 2}=\dfrac{24}{-50}$
$\dfrac{12}{-25}=\dfrac{12:(-1)}{-25:(-1)}=\dfrac{-24}{50}$
c.Ta có:
$\dfrac{18}{-48}=\dfrac{18\cdot 2}{-48\cdot 2}=\dfrac{36}{-96}$
$\dfrac{18}{-48}=\dfrac{18:6}{-48:6}=\dfrac{3}{-8}$
d.Ta có:
$\dfrac{-42}{-24}=\dfrac{-42\cdot (-1)}{-24\cdot (-1)}=\dfrac{42}{24}$
$\dfrac{-42}{-24}=\dfrac{-42:(-2)}{-24:(-2)}=\dfrac{21}{12}$
