Mình chỉ làm những câu phức tạp thôi nhé
r, $\frac{(x-2)^2}{12}-\frac{(x+1)^2}{21}=\frac{(x-4).(x-6)}{28}$
⇔ $\frac{7(x-2)^2}{84}-\frac{4(x+1)^2}{84}=\frac{3(x-4).(x-6)}{84}$
⇒ $7(x-2)^2-4(x+1)^2=3.(x-4).(x-6)$
⇔ $7x²-28x+28-4x²-8x-4=3x²-30x+72$
⇔ $-6x=48$
⇔ $x=-8$
u, $\frac{3(2x+1)}{4}-\frac{5x+3}{6}+\frac{x+1}{3}=x+\frac{7}{12}$
⇔ $\frac{9(2x+1)}{12}-\frac{2.(5x+3)}{12}+\frac{4.(x+1)}{12}=\frac{12x+7}{12}$
⇒ $9(2x+1)-2(5x+3)+4(x+1)=12x+7$
⇔ $12x+7=12x+7$
⇒ $x∈R$
x, $\frac{392-x}{32}+\frac{390-x}{34}+\frac{388-x}{36}+\frac{386-x}{38}+\frac{384-x}{40}=-5$
⇔ $\frac{392-x}{32}+1+\frac{390-x}{34}+1+\frac{388-x}{36}+1+\frac{386-x}{38}+1+\frac{384-x}{40}+1=0$
⇔ $(424-x).(\frac{1}{32}+\frac{1}{34}+\frac{1}{36}+\frac{1}{38}+\frac{1}{40})=0$
⇒ $424-x=0$
⇔ $x=424$
