$\frac{1}{2}^{x}$ + $\frac{1}{2}^{x+4}$ = 17
⇔ $(\frac{1}{2})^{x}$ +$(\frac{1}{2})^{x}$.$(\frac{1}{2})^{4}$ = 17
⇔ $(\frac{1}{2})^{x}$.[ 1 + $(\frac{1}{2})^{4}$ ] = 17
⇔ $(\frac{1}{2})^{x}$.$\frac{17}{16}$ = 17
⇔ $(\frac{1}{2})^{x}$ = 17 ÷ $\frac{17}{16}$
⇔ $(\frac{1}{2})^{x}$ = 17.$\frac{16}{17}$
⇔ $(\frac{1}{2})^{x}$ = 16 = 1.16 = 1÷$\frac{1}{16}$
= $\frac{1}{\frac{1}{16}}$
= $\frac{1}{(\frac{1}{2})^{4}}$
= $(\frac{1}{2})^{-4}$
⇒ x = -4
Vậy x = -4
