To find the perimeter of the triangle with vertices at the points \( A(1,5) \), \( B(4,1) \), and \( C(-4,-5) \), Nathan should follow these steps:
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Calculate the lengths of the sides of the triangle \( AB \), \( BC \), and \( CA \) using the distance formula. The distance \( d \) between two points \( (x_1, y_1) \) and \( (x_2, y_2) \) is given by the formula: \[ d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2} \]
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Calculate the length of side \( AB \):
- Coordinates of \( A \) are \( (1,5) \) and \( B \) are \( (4,1) \): \[ AB = \sqrt{(4 - 1)^2 + (1 - 5)^2} \] \[ = \sqrt{(3)^2 + (-4)^2} \] \[ = \sqrt{9 + 16} = \sqrt{25} = 5 \]
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Calculate the length of side \( BC \):
- Coordinates of \( B \) are \( (4,1) \) and \( C \) are \( (-4,-5) \): \[ BC = \sqrt{((-4) - 4)^2 + ((-5) - 1)^2} \] \[ = \sqrt{(-8)^2 + (-6)^2} \] \[ = \sqrt{64 + 36} = \sqrt{100} = 10 \]
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Calculate the length of side \( CA \):
- Coordinates of \( C \) are \( (-4,-5) \) and \( A \) are \( (1,5) \): \[ CA = \sqrt{(1 - (-4))^2 + (5 - (-5))^2} \] \[ = \sqrt{(1 + 4)^2 + (5 + 5)^2} \] \[ = \sqrt{(5)^2 + (10)^2} \] \[ = \sqrt{25 + 100} = \sqrt{125} = 5\sqrt{5} \approx 11.1803 \]
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Add the lengths of the sides to find the perimeter: \[ \text{Perimeter} = AB + BC + CA \] \[ = 5 + 10 + 5\sqrt{5} \approx 5 + 10 + 11.1803 = 26.1803 \]
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Round the perimeter to the nearest tenth: \[ \approx 26.2 \]
In summary, Nathan finds the lengths of each side using the distance formula, adds the lengths to calculate the perimeter, and rounds the result to the nearest tenth. The final answer is that the perimeter of the triangle is approximately 26.2 units.