If [tex]\( T: \mathbb{R}^2 \longrightarrow \mathbb{R}^2 \)[/tex] is a reflection in the line [tex]\( y = -3x \)[/tex], then [tex]\( T \left( \begin{array}{c} 2 \\ -3 \end{array} \right) \)[/tex] is:

(i) [tex]\( \left( \begin{array}{c} \frac{1}{5} \\ -\frac{18}{5} \end{array} \right) \)[/tex]

(ii) [tex]\( \left( \begin{array}{c} \frac{18}{5} \\ \frac{6}{5} \end{array} \right) \)[/tex]

(iii) [tex]\( \left( \begin{array}{c} -\frac{1}{5} \\ \frac{6}{5} \end{array} \right) \)[/tex]

(iv) [tex]\( \left( \begin{array}{c} \frac{1}{5} \\ -\frac{6}{5} \end{array} \right) \)[/tex]



Answer :

To determine the reflection of the point [tex]\(\left(2, -3\right)\)[/tex] in the line [tex]\( y = -3x \)[/tex], we need to follow several steps involving the general formula for reflection across a line of the form [tex]\( ax + by + c = 0 \)[/tex].

1. Identify the line equation in standard form:
The line [tex]\( y = -3x \)[/tex] can be rewritten in the standard form [tex]\( ax + by + c = 0 \)[/tex]:
[tex]\[ y + 3x = 0 \][/tex]
Here, [tex]\( a = 3 \)[/tex], [tex]\( b = 1 \)[/tex], and [tex]\( c = 0 \)[/tex].

2. General formula for reflection:
If [tex]\( (x_1, y_1) \)[/tex] is the original point and [tex]\( (x_2, y_2) \)[/tex] is the reflected point, the reflection formulas are:
[tex]\[ x_2 = x_1 - \frac{2a(ax_1 + by_1 + c)}{a^2 + b^2} \][/tex]
[tex]\[ y_2 = y_1 - \frac{2b(ax_1 + by_1 + c)}{a^2 + b^2} \][/tex]

3. Calculate each part:

First, calculate the denominator, which is [tex]\( a^2 + b^2 \)[/tex]:
[tex]\[ a^2 + b^2 = 3^2 + 1^2 = 9 + 1 = 10 \][/tex]

Next, calculate [tex]\( ax_1 + by_1 + c \)[/tex]:
[tex]\[ ax_1 + by_1 + c = 3(2) + 1(-3) + 0 = 6 - 3 = 3 \][/tex]

4. Substitute into the formulas for [tex]\( x_2 \)[/tex] and [tex]\( y_2 \)[/tex]:

[tex]\[ x_2 = 2 - \frac{2 \cdot 3 \cdot 3}{10} = 2 - \frac{18}{10} = 2 - 1.8 = 0.2 \][/tex]

[tex]\[ y_2 = -3 - \frac{2 \cdot 1 \cdot 3}{10} = -3 - \frac{6}{10} = -3 - 0.6 = -3.6 \][/tex]

5. Transform the result back to fraction form:

[tex]\[ 0.2 = \frac{1}{5} \][/tex]

[tex]\[ -3.6 = -\frac{18}{5} \][/tex]

6. Conclusion:

The reflected point [tex]\( T\left[\begin{array}{c}2 \\ -3\end{array}\right] \)[/tex] is given by:
[tex]\[ T\left[\begin{array}{c}2 \\ -3\end{array}\right] = \left[\begin{array}{c}0.2 \\ -3.6\end{array}\right] = \left[\begin{array}{c}\frac{1}{5} \\ -\frac{18}{5}\end{array}\right] \][/tex]

Hence, the correct answer from the given options is:
[tex]\[ (i) \left[\begin{array}{c}1 / 5 \\ -18 / 5\end{array}\right] \][/tex]