Câu 16 :
$\frac{1}{3}$ x + $\frac{2}{5}$ (x + 1 ) = 0
=> $\frac{1}{3}$ x + $\frac{2}{5}$ . x + $\frac{2}{5}$ = 0
=> ( $\frac{1}{3}$ + $\frac{2}{5}$ ) . x = $\frac{-2}{5}$
=> $\frac{5+6}{15}$ . x = $\frac{-2}{5}$
=> $\frac{11}{15}$ . x = $\frac{-2}{5}$
=> x = $\frac{-2}{5}$ . $\frac{15}{11}$
=> x = $\frac{-6}{11}$
Vậy x = $\frac{-6}{11}$
Câu 17 :
2x² - 72 = 0
2x² = 72
x² = 36
=> x ∈ { 6 ; -6 }
Vậy x ∈ { 6 ; -6 }
