Help!
1. 2^(2x) + 4 =17 x (times) 2^ (x-1)
i have been taught to find a common expression and denote it as y
i.e. 3 ^2x -10 times 3 ^x + 9=0; y= 3^x
but do not know how to do that here
Note that $\displaystyle 2^{x-1} = 2^x \cdot 2^{-1} = \frac{1}{2}\,2^x$
$\displaystyle 2^{2x} + 4 = \frac{17}{2} \cdot 2^x$
$\displaystyle 2^{2x} - \frac{17}{2}\,2^x + 4 =0$
This is now in the form of a quadratic equation in $\displaystyle 2^x$ so you can use the quadratic formula.
Recall that for all real x: $\displaystyle 2^x > 0$