Giải thích các bước giải:
Ta có:
a) $y-1=\frac{2}{3}-\frac{1}{7}$
$⇔y-1=\frac{11}{21}$
$⇔y=\frac{11}{21}+1$
$⇔y=\frac{11}{21}+\frac{21}{21}$
$⇔y=\frac{32}{21}$
Vậy $y=\frac{32}{21}$
b) $(1+2+3+.....+100)×(36×333-108×111)$
$=(1+2+3+....+100)×(36×333-36×3×111)$
$=(1+2+3+....+100)×(36×333-36×333)$
$=(1+2+3+....+100)×0$
$=0$
c) $\frac{7}{9}+\frac{2}{3}÷\frac{4}{9}$
$=\frac{7}{9}+\frac{2}{3}×\frac{9}{4}$
$=\frac{7}{9}+\frac{18}{12}$
$=\frac{7}{9}+\frac{3}{2}$
$=\frac{14}{18}+\frac{27}{18}$
$=\frac{41}{18}=1\frac{11}{21}$
d)$[77-(3×y+12)]=12$
$⇔77-(3×y+12)=12$
$⇔-(3×y+12)=12-77$
$⇔-(3×y+12)=-65$
$⇔3×y+12=65$
$⇔3×y=65-12=53$
$⇔y=\frac{53}{3}$
Vậy $y=\frac{53}{3}$
Chúc bạn học tốt ^-^
