2 câu trả lời
Lời giải:
$-\dfrac8{18}-\dfrac{15}{27}$
$=-\dfrac{8.3}{18.3}-\dfrac{15.2}{27.2}$
$=-\dfrac{24}{54} -\dfrac{ 30}{54}$
$=-\dfrac{54}{54}=-1$
$3,5-\left({-\dfrac27}\right)$
$=3,5+\dfrac27$
$=\dfrac72 + \dfrac27$
$=\dfrac{49}{14}+\dfrac4{14}$
$=\dfrac{53}{14}$
Giải thích:
Quy đồng mẫu số chung.
-8/18-15/27=-24/54-30/54=-54/54=-1
3,5-(-2/7)=3,5+2/7=7/2+2/7=49/14+4/14=53/14
