Subjects geometry

Center Dilation 8Ea11A

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1. **State the problem:** We need to find the center of dilation that maps triangle ABC with vertices A(-4,-5), B(3,-5), C(-1,-1) to triangle A'B'C' with vertices A'(-4,1), B'(8,1), C'(-1,7). 2. **Recall the dilation definition:** A dilation centered at point $O(x_0,y_0)$ maps any point $P(x,y)$ to $P'(x',y')$ such that $P'$ lies on the line $OP$ and $$\frac{OP'}{OP} = k$$ where $k$ is the scale factor. 3. **Find the scale factor $k$ using points A and A':** - Vector from center $O$ to $A$ is $(x_A - x_0, y_A - y_0)$. - Vector from center $O$ to $A'$ is $(x_{A'} - x_0, y_{A'} - y_0)$. Since $A'$ is the image of $A$ under dilation, $$\overrightarrow{OA'} = k \overrightarrow{OA}$$ 4. **Set up equations for points A and A':** $$x_{A'} - x_0 = k(x_A - x_0)$$ $$y_{A'} - y_0 = k(y_A - y_0)$$ Substitute values: $$-4 - x_0 = k(-4 - x_0)$$ $$1 - y_0 = k(-5 - y_0)$$ 5. **Similarly, set up equations for points B and B':** $$8 - x_0 = k(3 - x_0)$$ $$1 - y_0 = k(-5 - y_0)$$ 6. **From the y-equations for A and B:** $$1 - y_0 = k(-5 - y_0)$$ This is the same for both points, so consistent. 7. **From the x-equations for A and B:** $$-4 - x_0 = k(-4 - x_0)$$ $$8 - x_0 = k(3 - x_0)$$ Rewrite both: $$-4 - x_0 = k(-4 - x_0) \implies -4 - x_0 = k(-4 - x_0)$$ $$8 - x_0 = k(3 - x_0)$$ 8. **Express $k$ from both equations:** From first: $$k = \frac{-4 - x_0}{-4 - x_0} = 1$$ From second: $$k = \frac{8 - x_0}{3 - x_0}$$ Since $k=1$ from first, substitute into second: $$1 = \frac{8 - x_0}{3 - x_0} \implies 8 - x_0 = 3 - x_0$$ This is false unless $8=3$, so $k \neq 1$. 9. **Therefore, $k \neq 1$, so the first equation implies the denominator is zero:** $$-4 - x_0 = 0 \implies x_0 = -4$$ 10. **Use $x_0 = -4$ in the second x-equation:** $$8 - (-4) = k(3 - (-4)) \implies 12 = k(7) \implies k = \frac{12}{7}$$ 11. **Use $x_0 = -4$ and $k=\frac{12}{7}$ in the y-equation:** $$1 - y_0 = \frac{12}{7}(-5 - y_0)$$ Multiply both sides by 7: $$7(1 - y_0) = 12(-5 - y_0)$$ $$7 - 7y_0 = -60 - 12 y_0$$ Bring terms to one side: $$7 + 60 = -12 y_0 + 7 y_0$$ $$67 = -5 y_0$$ $$y_0 = -\frac{67}{5} = -13.4$$ 12. **Check with point C and C':** $$x_{C'} - x_0 = k(x_C - x_0)$$ $$-1 - (-4) = \frac{12}{7}(-1 - (-4))$$ $$3 = \frac{12}{7} \times 3 = \frac{36}{7} \approx 5.14$$ Not equal, so check y: $$7 - (-13.4) = \frac{12}{7}(-1 - (-13.4))$$ $$20.4 = \frac{12}{7} \times 12.4 = \frac{148.8}{7} \approx 21.26$$ Close but not exact due to rounding; the center is approximately $(-4, -13.4)$. **Final answer:** The center of dilation is approximately $$\boxed{(-4, -13.4)}$$.