a.

For
, we have by this definition
which is equal to
for
.
Assume
for some
. We want to use this to show that this implies
. By the recursive definition,

and we're done.
b.

For
, we have
, and
.
Assume
for some
. Then for
, we have

and we're done.
Step-by-step explanation:
12x + 3(x - 4) + 2x
17x-12
HOPE IT HELPS U