Question: enlarge the triangle by scale factor $-3$ with centre $(2,3)$
1. **Problem Statement:**
We need to enlarge the triangle with vertices at $(2,4)$, $(2,5)$, and $(4,5)$ by a scale factor of $-3$ centered at the point $(2,3)$.
2. **Formula for enlargement:**
If a point $P=(x,y)$ is enlarged by scale factor $k$ about center $C=(x_c,y_c)$, the new point $P'=(x',y')$ is given by:
$$
x' = x_c + k(x - x_c), \quad y' = y_c + k(y - y_c)
$$
3. **Apply the formula to each vertex:**
- For $A=(2,4)$:
$$
x'_A = 2 + (-3)(2 - 2) = 2 + (-3)(0) = 2$$
$$
y'_A = 3 + (-3)(4 - 3) = 3 + (-3)(1) = 3 - 3 = 0$$
So, $A' = (2,0)$.
- For $B=(2,5)$:
$$
x'_B = 2 + (-3)(2 - 2) = 2 + 0 = 2$$
$$
y'_B = 3 + (-3)(5 - 3) = 3 + (-3)(2) = 3 - 6 = -3$$
So, $B' = (2,-3)$.
- For $C=(4,5)$:
$$
x'_C = 2 + (-3)(4 - 2) = 2 + (-3)(2) = 2 - 6 = -4$$
$$
y'_C = 3 + (-3)(5 - 3) = 3 + (-3)(2) = 3 - 6 = -3$$
So, $C' = (-4,-3)$.
4. **Summary of new vertices:**
The enlarged triangle has vertices at:
$$
A' = (2,0), \quad B' = (2,-3), \quad C' = (-4,-3)
$$
5. **Interpretation:**
The triangle is scaled by a factor of $-3$ about $(2,3)$, which means it is enlarged by 3 times and reflected through the center point.
**Final answer:** The vertices of the enlarged triangle are $(2,0)$, $(2,-3)$, and $(-4,-3)$.