Đáp án:
$\displaystyle \begin{array}{{>{\displaystyle}l}} a.\ i.\ x=\frac{-39}{100}\\ ii.x=\frac{105}{8}\\ iii.x=\frac{169}{50}\\ iv.x=\frac{2}{7}\\ b.i.x=\frac{18}{5}\\ ii.x=\pm 12\\ iii.x=-11\\ iv.x=14\ hoặc\ x=-4 \end{array}$
Giải thích các bước giải:
$\displaystyle \begin{array}{{>{\displaystyle}l}} Bài\ 4B:\\ a.\ \\ i.\ 1,8:1,3=-2,7:5x\\ \Leftrightarrow \frac{9}{5} :\frac{13}{10} =\frac{-27}{10} :5x\\ \Leftrightarrow \frac{18}{13} =\frac{-27}{50x}\\ \Leftrightarrow 50x.18=-27.13\\ \Leftrightarrow x=\frac{-39}{100}\\ ii.\ 15:4=x:3,5\\ \Leftrightarrow \frac{15}{4} =\frac{2}{7} x\\ \Leftrightarrow x=\frac{105}{8}\\ iii.\ x:6,5=0,13:0,25\\ \Leftrightarrow \frac{2x}{13} =\frac{13}{25}\\ \Leftrightarrow x=\frac{169}{50}\\ iv.\ 5,25:x=3,6:2,4\\ \Leftrightarrow \frac{21}{4} x=\frac{3}{2}\\ \Leftrightarrow x=\frac{2}{7}\\ b.\ \\ i.\ \frac{x}{4} =\frac{9}{10}\\ \Leftrightarrow 10x=36\\ \Leftrightarrow x=\frac{18}{5}\\ ii.\ \frac{x}{24} =\frac{6}{x}\\ \Leftrightarrow x^{2} =144\\ \Leftrightarrow x=\pm 12\\ iii.\ \frac{5-2x}{3} =\frac{4x-1}{-5}\\ \Leftrightarrow -25+10x=12x-3\\ \Leftrightarrow 2x=-22\\ \Leftrightarrow x=-11\\ iv.\ \frac{10-2x}{6} =\frac{27}{5-x}\\ \Leftrightarrow 50\ -20x+2x^{2} =162\\ \Leftrightarrow 2x^{2} -20x-112=0\\ \Leftrightarrow ( x-14) .( x+4) =0\\ \Leftrightarrow x=14\ hoặc\ x=-4 \end{array}$
