Giúp mik với, mai mik phải nộp bài rồi. Bài 1:Tìm x biết a/ x+30% x=-1,3; b/ 5,5 x=13/15;c/ 2/3x-1/2x=5/12 Bài 2:So sánh a) 3/4 và 0,75 ;b) -2 1/2 và

Đáp án:

1.
$a)  x=-1\\
b) x=\frac{143}{30}\\
c) x=\frac{5}{2}\\
2.
a)0,75=\frac{3}{4}\\
b)  -2\frac{1}{2}>\frac{-5}{3}\\
c)  \frac{4}{9}-\frac{1}{2}<\frac{3}{7}\\$
d) $ \frac{77}{19}>\frac{116}{37}>\frac{134}{43}>\frac{55}{21}$

Giải thích các bước giải:

1.
$a) x+0,3x=-1,3\\
\Leftrightarrow (1+0,3)x=-1,3\\
\Leftrightarrow x=-1\\
b) 5,5x=\frac{13}{15}\\
\Leftrightarrow x=\frac{13.5,5}{15}=\frac{143}{30}\\
c) \frac{2}{3}x-\frac{1}{2}x=\frac{5}{12}\\
\Leftrightarrow \left ( \frac{2}{3}-\frac{1}{2} \right )x=\frac{5}{12}\\
\Leftrightarrow \frac{4-3}{6}x=\frac{5}{12}\\
\Leftrightarrow \frac{1}{6}x=\frac{5}{12}\\
\Leftrightarrow x=\frac{5.6}{12}=\frac{5}{2}\\
2.
a)0,75=\frac{75}{100}=\frac{3}{4}\\
b) -2\frac{1}{2}=\frac{-5}{2}$
Vì 2<3 nên $\frac{-5}{2}>\frac{-5}{3}\\
\Rightarrow -2\frac{1}{2}>\frac{-5}{3}\\
c) \frac{4}{9}-\frac{1}{2}=\frac{4.2-9}{9.2}=\frac{-1}{18}=\frac{(-1).7}{18.7}=\frac{-7}{126}\\
\frac{3}{7}=\frac{3.18}{7.18}=\frac{54}{126}$
Vì $-7<54\Rightarrow \frac{-7}{126}< \frac{54}{126}\\
\Rightarrow \frac{4}{9}-\frac{1}{2}<\frac{3}{7}\\
d) MSC=43.21.19.37\\
\frac{134}{43}=\frac{134.21.19.37}{43.21.19.37}=\frac{1978242}{634809}\\
\frac{55}{21}=\frac{55.43.19.37}{43.21.19.37}=\frac{1662595}{634809}\\
\frac{77}{19}=\frac{77.21.43.37}{43.21.19.37}=\frac{2572647}{634809}\\
\frac{116}{37}=\frac{116.21.19.43}{43.21.19.37}=\frac{1990212}{634809}$
Vì $2572647>1990212>1978242>1662595 \Rightarrow \frac{2572647}{634809}>\frac{1990212}{634809}>\frac{1978242}{634809}>\frac{1662595}{634809}\\
\Rightarrow \frac{77}{19}>\frac{116}{37}>\frac{134}{43}>\frac{55}{21}$