Giải thích các bước giải:
Bài 1:
a.Ta có:
$\dfrac{-3}{7}-(\dfrac23-\dfrac37)=-\dfrac37-\dfrac23+\dfrac37=\dfrac37-\dfrac37-\dfrac23=0-\dfrac23=-\dfrac23$
b.Ta có:
$\dfrac2{15}:(\dfrac13\cdot \dfrac45-\dfrac13\cdot \dfrac65)$
$=\dfrac2{15}:(\dfrac13\cdot( \dfrac45-\dfrac65))$
$=\dfrac2{15}:(\dfrac13\cdot \dfrac{4-6}5)$
$=\dfrac2{15}:(\dfrac13\cdot \dfrac{-2}5)$
$=\dfrac2{15}: \dfrac{-2}{15}$
$=-\dfrac2{15}: \dfrac{2}{15}$
$=-1$
Bài 2:
a.Ta có:
$\dfrac34+\dfrac14x=\dfrac58$
$\to \dfrac14x=\dfrac58-\dfrac34$
$\to\dfrac14x=-\dfrac18$
$\to x=-\dfrac12$
b.Ta có:
$25\%x+x=-1.25$
$\to 0.25x+x=-1.25$
$\to x(0.25+1)=-1.25$
$\to x\cdot 1.25=-1.25$
$\to x=-1$
