Vector Linear Combination
1. The problem is to express the vector \(\overline{x}\) as a linear combination of vectors \(\overline{p}, \overline{q}, \overline{r}\), i.e., find scalars \(a, b, c\) such that
$$\overline{x} = a\overline{p} + b\overline{q} + c\overline{r}.$$
2. This translates to a system of linear equations:
$$a p_1 + b q_1 + c r_1 = x_1,$$
$$a p_2 + b q_2 + c r_2 = x_2,$$
$$a p_3 + b q_3 + c r_3 = x_3,$$
where the subscripts represent the components of the vectors.
3. We form the coefficient matrix and solve for \((a, b, c)\):
\[
\begin{pmatrix}p_1 & q_1 & r_1 \\
p_2 & q_2 & r_2 \\
p_3 & q_3 & r_3
\end{pmatrix}
\begin{pmatrix}a\\b\\c\end{pmatrix} =
\begin{pmatrix}x_1\\x_2\\x_3\end{pmatrix}
\]
4. Solve using matrix inversion if possible or substitution/row reduction.
5. Specifically for problem 8:
\(\overline{x} = (3, 3, -1), \overline{p} = (3, 1, 0), \overline{q} = (-1, 2, 1), \overline{r} = (-1, 0, 2)\)
Set up system:
$$3a -1b -1c = 3$$
$$1a + 2b + 0c = 3$$
$$0a + 1b + 2c = -1$$
6. From equation 2:
$$a + 2b = 3 \Rightarrow a = 3 - 2b.$$
7. From equation 3:
$$b + 2c = -1 \Rightarrow b = -1 - 2c.$$
8. Substitute \(a, b\) into equation 1:
$$3(3 - 2b) - b - c = 3.$$
Substitute \(b = -1 - 2c\):
$$3(3 - 2(-1 - 2c)) - (-1 - 2c) - c = 3.$$
Simplify inside:
$$3(3 + 2 + 4c) + 1 + 2c - c = 3,$$
$$3(5 + 4c) + 1 + c = 3,$$
$$15 + 12c + 1 + c = 3,$$
$$16 + 13c = 3,$$
$$13c = 3 - 16 = -13,$$
$$c = -1.$$
9. Back substitute \(c = -1\) into \(b = -1 - 2c = -1 - 2(-1) = -1 + 2 = 1\).
10. Back substitute \(b = 1\) into \(a = 3 - 2b = 3 - 2(1) = 1\).
Answer:
$$\boxed{\overline{x} = 1 \cdot \overline{p} + 1 \cdot \overline{q} + (-1) \cdot \overline{r}}.$$