[tex]$\triangle ABC$[/tex] is reflected across the [tex]$y$[/tex]-axis and then dilated by a factor of 3 using the point [tex]$(-1,2)$[/tex] as the center of dilation. What is the transformation of [tex]$B(5,3)$[/tex]?

A. [tex]$B^{\prime \prime}(-15,9)$[/tex]
B. [tex]$B^{\prime}(-5,3)$[/tex]
C. [tex]$B^{\prime}(-4,1)$[/tex]
D. [tex]$B^{\prime}(-13,5)$[/tex]



Answer :

Let's solve the transformation of point [tex]\( B(5,3) \)[/tex] step by step.

### Step 1: Reflection across the y-axis
First, we reflect point [tex]\( B(5,3) \)[/tex] across the y-axis. Reflecting across the y-axis changes the sign of the x-coordinate while the y-coordinate remains the same.

[tex]\[ B'(x', y') \quad \text{where} \quad x' = -x \quad \text{and} \quad y' = y \][/tex]

So,
[tex]\[ B'(x', y') = (-5, 3) \][/tex]

### Step 2: Dilation with center [tex]\((-1, 2)\)[/tex] and factor of 3
Next, we dilate [tex]\( B'(-5,3) \)[/tex] with the center of dilation at [tex]\((-1,2)\)[/tex] and a dilation factor of 3.

The formula for dilation with a specific center [tex]\((c_x, c_y)\)[/tex] and factor [tex]\( k \)[/tex] is:

[tex]\[ (x'', y'') = \left( c_x + k(x' - c_x) , c_y + k(y' - c_y) \right) \][/tex]

Substituting the values [tex]\( c_x = -1 \)[/tex], [tex]\( c_y = 2 \)[/tex], [tex]\( x' = -5 \)[/tex], [tex]\( y' = 3 \)[/tex], and [tex]\( k = 3 \)[/tex], we get:

[tex]\[ x'' = -1 + 3(-5 + 1) = -1 + 3(-4) = -1 - 12 = -13 \][/tex]

[tex]\[ y'' = 2 + 3(3 - 2) = 2 + 3(1) = 2 + 3 = 5 \][/tex]

Hence,
[tex]\[ B''(-13, 5) \][/tex]

Now, let's identify the correct option:
D. [tex]\( B''(-13, 5) \)[/tex] is the correct answer.

Thus, the transformation of [tex]\( B(5,3) \)[/tex] after reflection across the y-axis and dilation by a factor of 3 using the point [tex]\((-1,2)\)[/tex] as the center of dilation is [tex]\( \boxed{(-13,5)} \)[/tex].