Đáp án:
a, x : $\frac{6}{7}$ = $\frac{7}{8}$
x = $\frac{7}{8}$ × $\frac{6}{7}$
⇒ x = $\frac{3}{4}$
Vậy x = $\frac{3}{4}$
b.| x - $\frac{3}{10}$ | - $\frac{6}{5}$ = $\frac{11}{10}$
| x - $\frac{3}{10}$ | = $\frac{11}{10}$ + $\frac{6}{5}$
| x - $\frac{3}{10}$ | = $\frac{11}{10}$ + $\frac{12}{10}$
| x - $\frac{3}{10}$ | = $\frac{23}{10}$
⇒ x - $\frac{3}{10}$ = ( $\frac{-23}{10}$ ; $\frac{23}{10}$ )
TH1: x - $\frac{3}{10}$ = $\frac{-23}{10}$
x = $\frac{-23}{10}$+ $\frac{3}{10}$
x = $\frac{- 20}{10}$
x = -2
TH2: x - $\frac{3}{10}$ = $\frac{23}{10}$
x = $\frac{23}{10}$+ $\frac{3}{10}$
x = $\frac{- 26}{10}$
x = $\frac{- 13}{5}$
Vậy x ∈ { -2 ; $\frac{- 13}{5}$ }
