Giải thích các bước giải:
Phần 1
Câu 1.D
Câu 2.A
Câu 3.B
Câu 4.C
Phần 2
Bài 1
a)$\frac{19}{5}$.$\frac{7}{13}$+$\frac{9}{13}$.$\frac{19}{5}$-$\frac{19}{5}$.$\frac{3}{13}$
=$\frac{19}{5}$.$\frac{7}{13}$+$\frac{9}{13}$.$\frac{19}{5}$+$\frac{-19}{5}$.$\frac{3}{13}$
=$\frac{19}{5}$.$\frac{7}{13}$+$\frac{9}{13}$.$\frac{19}{5}$+$\frac{19}{5}$.$\frac{-3}{13}$
=$\frac{19}{5}$.( $\frac{7}{13}$+$\frac{9}{13}$+$\frac{-3}{13}$)
=$\frac{19}{5}$.$\frac{13}{13}$=$\frac{19}{5}$.1
=$\frac{19}{5}$
b)$\frac{-1}{6}$.$\frac{3}{5}$ =$\frac{-3}{30}$= $\frac{-1}{10}$
c)-1,4.$\frac{15}{-49}$-(40%+$\frac{4}{3}$):2$\frac{3}{5}$
=$\frac{-7}{5}$.$\frac{-15}{49}$-($\frac{2}{5}$+$\frac{4}{3}$):$\frac{13}{5}$
=$\frac{3}{7}$-($\frac{6}{15}$+$\frac{20}{15}$):$\frac{13}{5}$
=$\frac{3}{7}$-$\frac{26}{15}$.$\frac{5}{13}$
=$\frac{3}{7}$-$\frac{2}{3}$
=$\frac{9}{21}$- $\frac{14}{21}$
=$\frac{-5}{21}$
Bài 2
a)x-$\frac{1}{3}$=$\frac{1}{2}$
x=$\frac{1}{2}$+$\frac{1}{3}$
x=$\frac{5}{6}$
b)$\frac{x}{21}$-$\frac{2}{3}$=$\frac{5}{21}$
$\frac{x}{21}$=$\frac{5}{21}$+$\frac{2}{3}$
$\frac{x}{21}$=$\frac{19}{21}$
x =19
c)$\frac{4}{5}$+$\frac{5}{7}$:x=$\frac{1}{6}$
$\frac{5}{7}$:x=$\frac{1}{6}$-$\frac{4}{5}$
$\frac{5}{7}$:x=$\frac{-19}{30}$
x =$\frac{5}{7}$:$\frac{-19}{30}$
x =$\frac{-150}{133}$
d)$(3x+1)^{2}$.$\frac{-1}{4}$=$\frac{-49}{4}$
$(3x+1)^{2}$= $\frac{-49}{4}$:$\frac{-1}{4}$
$(3x+1)^{2}$=49
$(3x+1)^{2}$=$7^{2}$
3x =7-1
3x =6
x =6:3
x =2
