(8) The solution to the equation $3 \cdot 16^{x}+2 \cdot 81^{x}=5 \cdot 36^{x}$ is
$80, \frac{1}{2}$ Hint: The original equation can be transformed into $3 \cdot\left(4^{x}\right)^{2}-5 \cdot 4^{x} \cdot 9^{x}+2 \cdot\left(9^{x}\right)^{2}=$ 0 . Dividing both sides by $\left(9^{x}\right)^{2}$, we get
$$
3\left[\left(\frac{4}{9}\right)^{x}\right]^{2}-5 \cdot\left(\frac{4}{9}\right)^{x}+2=0 .
$$

Let $\left(\frac{4}{9}\right)^{x}=t$, further transforming it into $3 t^{2}-5 t+2=0$. Solving this, we get $t_{1}=1$, $t_{2}=\frac{2}{3}$. That is, $\left(\frac{4}{9}\right)^{x}=1$ or $\left(\frac{4}{9}\right)^{x}=\frac{2}{3}, x=0$ or $\frac{1}{2}$.