Giui toi voi moi nguoi oi

Giải thích các bước giải:

 a)$(3x-2)^2=81$
⇔$\left[ \begin{array}{l}3x-2=9\\3x-2=-9\end{array} \right.$
⇔$\left[ \begin{array}{l}x=\dfrac{11}{3}\\x=-\dfrac{7}{3}\end{array} \right.$
b) $(2x+1)^3=64$
⇔$2x+1=4$
⇔$x=\dfrac{3}{2}$
c)
d)$7^{x+2}+2.7^{x-1}=345$
⇔$7^{x-1}(7^3+2)=345$
⇔$7^{x-1}=1$
⇔$x-1=0$
⇔$x=1$