Concept:
Since \(T\) is linear,
\[
T(\alpha u+\beta v)=\alpha T(u)+\beta T(v)
\]
We express \((5,6)\) as a linear combination of \((1,2)\) and \((0,1)\).
Step 1: Express \((5,6)\).
Let
\[
(5,6)=a(1,2)+b(0,1)
\]
Then,
\[
a(1,2)+b(0,1)=(a,2a+b)
\]
So,
\[
a=5
\]
and
\[
2a+b=6
\]
Substitute \(a=5\):
\[
10+b=6
\]
\[
b=-4
\]
Thus,
\[
(5,6)=5(1,2)-4(0,1)
\]
Step 2: Apply linearity.
\[
T(5,6)=5T(1,2)-4T(0,1)
\]
\[
=5(2,3)-4(1,4)
\]
\[
=(10,15)-(4,16)
\]
\[
=(6,-1)
\]
Step 3: Final answer.
\[
\boxed{(6,-1)}
\]