# Thread: Linear Transformations

1. ## Linear Transformations

Let u = (1,2), v = (3,1) and T: $R^{2}\rightarrow R$ be a linear transformation such that T(u)= 4 and T(v)= 5. What is T(-3, 4)? (Hint: Write (-3,4) as a linear combination of u and v.)

I don't really know where to start. I know I have to write (-3,4) as a linear combination of u and v, but what do I do from there?

2. $
S=[\vec{u},\vec{v}],\begin{bmatrix}-3\\4\end{bmatrix}=S(S^{-1}\begin{bmatrix}-3\\4\end{bmatrix})=[\vec{u},\vec{v}]\begin{bmatrix}3\\-2\end{bmatrix}= 3\vec{u} -2\vec{v}$

$
T(\begin{bmatrix}-3\\4\end{bmatrix})=T(3\vec{u} -2\vec{v})=3T(\vec{u})-2T(\vec{v})=3\times 4-2\times 5=2
$

3. Originally Posted by temaire
Let u = (1,2), v = (3,1) and T: $R^{2}\rightarrow R$ be a linear transformation such that T(u)= 4 and T(v)= 5. What is T(-3, 4)? (Hint: Write (-3,4) as a linear combination of u and v.)

I don't really know where to start. I know I have to write (-3,4) as a linear combination of u and v, but what do I do from there?
Once you have (-3, 4)= au+ bv, T((-3,4))= aT(u)+ bT(v)= 4a+ 5b.