Linear Transformation Matrix
1. **Stating the problem:**
We have a linear transformation $$T : \mathbb{P}_2(\mathbb{R}) \to \mathbb{P}_3(\mathbb{R})$$ defined by
$$T(p(x)) = p'(x) + \int_0^x p(t) \, dt,$$
where $$\mathbb{P}_n(\mathbb{R})$$ is the space of real polynomials of degree at most $$n$$. We want to verify which statements (a, b, c, d, e) about $$T$$ and its standard matrix representations are true.
2. **Find the matrix representation of $$T$$ relative to the bases $$\{1, x, x^2\}$$ and $$\{1, x, x^2, x^3\}$$:**
Let $$p(x) = a + bx + cx^2$$.
- Compute the derivative:
$$p'(x) = b + 2cx.$$
- Compute the integral from 0 to $$x$$:
$$\int_0^x p(t) \, dt = \int_0^x (a + bt + ct^2) \, dt = a x + \frac{b}{2} x^2 + \frac{c}{3} x^3.$$
- So,
$$T(p(x)) = p'(x) + \int_0^x p(t) \, dt = (b) + (2c x) + \left(a x + \frac{b}{2} x^2 + \frac{c}{3} x^3\right) = b + (2c + a) x + \frac{b}{2} x^2 + \frac{c}{3} x^3.$$
3. **Express this as a vector with respect to the $$\{1, x, x^2, x^3\}$$ basis:**
$$T(p(x)) = \begin{pmatrix} b \\ a + 2c \\ \frac{b}{2} \\ \frac{c}{3} \end{pmatrix}.$$
4. **Find the matrix columns by applying $$T$$ to each basis vector of $$\mathbb{P}_2$$:**
- $$T(1) = 0 + \int_0^x 1 \, dt = x = 0 \cdot 1 + 1 \cdot x + 0 \cdot x^2 + 0 \cdot x^3$$ gives the first column $$\begin{pmatrix}0 \\ 1 \\ 0 \\ 0\end{pmatrix}$$.
- $$T(x) = 1 + \int_0^x t \, dt = 1 + \frac{x^2}{2} = 1 \cdot 1 + 0 \cdot x + \frac{1}{2} x^2 + 0 \cdot x^3$$ gives the second column $$\begin{pmatrix}1 \\ 0 \\ \frac{1}{2} \\ 0\end{pmatrix}$$.
- $$T(x^2) = 2x + \int_0^x t^2 \, dt = 2x + \frac{x^3}{3} = 0 \cdot 1 + 2 \cdot x + 0 \cdot x^2 + \frac{1}{3} x^3$$ gives the third column $$\begin{pmatrix}0 \\ 2 \\ 0 \\ \frac{1}{3}\end{pmatrix}$$.
5. **Construct the standard matrix of $$T$$:**
$$\begin{pmatrix} 0 & 1 & 0 \\ 1 & 0 & 2 \\ 0 & \frac{1}{2} & 0 \\ 0 & 0 & \frac{1}{3} \end{pmatrix}.$$ This matches option (a).
6. **Check injectivity (one-to-one):**
The domain $$\mathbb{P}_2$$ has dimension 3, codomain $$\mathbb{P}_3$$ has dimension 4.
- Suppose $$T(p) = 0$$. Then
$$b = 0,$$
$$a + 2c = 0,$$
$$\frac{b}{2} = 0$$ (already zero),
$$\frac{c}{3} = 0 \implies c=0.$$
From $$a + 2c = a = 0$$.
So $$a=b=c=0$$ means only the zero polynomial maps to zero; hence, $$T$$ is injective.
7. **Check surjectivity (onto):**
Since the codomain dimension (4) is greater than the domain dimension (3), $$T$$ cannot be onto.
8. **Is $$T$$ an isomorphism?**
No, because it is not onto.
9. **Option (e) matrix check:**
The matrix in (e) has $$\frac{1}{3}$$ replaced by $$\frac{1}{3}$$ with $$\frac{1}{3}$$ changed to $$\frac{1}{4}$$ in the last entry, which does not match our computed matrix, so (e) is false.
**Summary:**
- (a) True.
- (b) True.
- (c) False.
- (d) False.
- (e) False.