Giải câu 2 trang 43 Cánh Diều Toán 6 tập 2.
a) $\frac{-2}{3}$ . $\frac{[?]}{4}$ = $\frac{1}{2}$
$\frac{[?]}{4}$ = $\frac{1}{2}$ : $\frac{-2}{3}$
$\frac{[?]}{4}$ = $\frac{1}{2}$ . $\frac{3}{- 2}$
$\frac{[?]}{4}$ = $\frac{1 . 3}{2 . (-2)}$
$\frac{[?]}{4}$ = $\frac{- 3}{4}$
=> [?] = - 3
b) $\frac{[?]}{3}$ . $\frac{5}{8}$ = $\frac{-5}{12}$
$\frac{[?]}{3}$ = $\frac{-5}{12}$ : $\frac{5}{8}$
$\frac{[?]}{3}$ = $\frac{-5}{12}$ . $\frac{8}{5}$
$\frac{[?]}{3}$ = $\frac{(-5) . 8}{12 . 5}$
$\frac{[?]}{3}$ = $\frac{- 40}{60}$
$\frac{[?]}{3}$ = $\frac{- 2}{3}$
=> [?] = - 2
c) $\frac{5}{6}$ . $\frac{3}{[?]}$ = $\frac{1}{4}$
$\frac{3}{[?]}$ = $\frac{1}{4}$ : $\frac{5}{6}$
$\frac{3}{[?]}$ = $\frac{1}{4}$ . $\frac{6}{5}$
$\frac{3}{[?]}$ = $\frac{1 . 6}{4 . 5}$
$\frac{3}{[?]}$ = $\frac{6}{20}$
$\frac{3}{[?]}$ = $\frac{3}{10}$
=> [?] = 10