Problem B3 (b) says "Given \(f(x)= log_2(x)- 3\) solve the following for x: \(f^{-1}(x-1)= 4^x+3\)." Actually it isn't necessary to find \(f^{-1}\). Taking \(f\) of both sides gives \(f(f^{-1}(x- 1))= x- 1= log_2(4^x+ 3)\).
We can write this as \(2^{x- 1}= 2^x/2= 4^x+ 3= 2^{2x}+ 3\). Let \(y= 2^x\) so this becomes \(y/2= y^2+ 3\) or \(2y^2- y+ 6= 0\). Solve that using the quadratic equation then solve \(2^x= y\) for \(x\).
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