\(y=a\cdot b^x\quad,\quad b>0\)
a)
\(128=2 b^3\\
b^3=64\\
b=4\\\\
y=2\cdot4^x\)
b)
\(4=a\cdot b^0\\
1=a\cdot b^2\\\\
a=4\\
1=a\cdot b^2\\\\
1=4\cdot b^2\\
b^2=\dfrac{1}{4}\\
b=\dfrac{1}{2} \vee b=-\dfrac{1}{2}\\
-\dfrac{1}{2}<0 \Rightarrow b=\dfrac{1}{2}\\\\
y=4\cdot \left(\dfrac{1}{2}\right)^x\)
