Math Problem Statement

Find the coordinates of the incentre of the triangle whose vertices are (a) (4, –2) (–2, 4) (5, 5)

Solution

To find the coordinates of the incenter of a triangle, we can use the formula:

I(x,y)=(aAx+bBx+cCxa+b+c,aAy+bBy+cCya+b+c)I(x, y) = \left( \frac{aA_x + bB_x + cC_x}{a + b + c}, \frac{aA_y + bB_y + cC_y}{a + b + c} \right)

Where:

  • A(x1,y1)A(x_1, y_1), B(x2,y2)B(x_2, y_2), and C(x3,y3)C(x_3, y_3) are the coordinates of the triangle's vertices.
  • aa, bb, and cc are the lengths of the sides opposite to vertices AA, BB, and CC, respectively.

Step 1: Find the lengths of the sides

We can use the distance formula to calculate the lengths of the sides: Distance between two points=(x2x1)2+(y2y1)2\text{Distance between two points} = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}

  1. Side aa (opposite vertex AA): Between points B(2,4)B(-2, 4) and C(5,5)C(5, 5): a=(25)2+(45)2=(7)2+(1)2=49+1=50=52a = \sqrt{(-2 - 5)^2 + (4 - 5)^2} = \sqrt{(-7)^2 + (-1)^2} = \sqrt{49 + 1} = \sqrt{50} = 5\sqrt{2}

  2. Side bb (opposite vertex BB): Between points A(4,2)A(4, -2) and C(5,5)C(5, 5): b=(45)2+(25)2=(1)2+(7)2=1+49=50=52b = \sqrt{(4 - 5)^2 + (-2 - 5)^2} = \sqrt{(-1)^2 + (-7)^2} = \sqrt{1 + 49} = \sqrt{50} = 5\sqrt{2}

  3. Side cc (opposite vertex CC): Between points A(4,2)A(4, -2) and B(2,4)B(-2, 4): c=(4(2))2+(24)2=(6)2+(6)2=36+36=72=62c = \sqrt{(4 - (-2))^2 + (-2 - 4)^2} = \sqrt{(6)^2 + (-6)^2} = \sqrt{36 + 36} = \sqrt{72} = 6\sqrt{2}

Step 2: Apply the formula for the incenter

We now substitute the values into the formula for the incenter:

I(x,y)=(aAx+bBx+cCxa+b+c,aAy+bBy+cCya+b+c)I(x, y) = \left( \frac{aA_x + bB_x + cC_x}{a + b + c}, \frac{aA_y + bB_y + cC_y}{a + b + c} \right)

Substitute the known values:

a=52,b=52,c=62a = 5\sqrt{2}, \quad b = 5\sqrt{2}, \quad c = 6\sqrt{2} A(4,2),B(2,4),C(5,5)A(4, -2), \quad B(-2, 4), \quad C(5, 5)

x=52×4+52×(2)+62×552+52+62=202102+302162=402162=2.5x = \frac{5\sqrt{2} \times 4 + 5\sqrt{2} \times (-2) + 6\sqrt{2} \times 5}{5\sqrt{2} + 5\sqrt{2} + 6\sqrt{2}} = \frac{20\sqrt{2} - 10\sqrt{2} + 30\sqrt{2}}{16\sqrt{2}} = \frac{40\sqrt{2}}{16\sqrt{2}} = 2.5

y=52×(2)+52×4+62×552+52+62=102+202+302162=402162=2.5y = \frac{5\sqrt{2} \times (-2) + 5\sqrt{2} \times 4 + 6\sqrt{2} \times 5}{5\sqrt{2} + 5\sqrt{2} + 6\sqrt{2}} = \frac{-10\sqrt{2} + 20\sqrt{2} + 30\sqrt{2}}{16\sqrt{2}} = \frac{40\sqrt{2}}{16\sqrt{2}} = 2.5

Thus, the coordinates of the incenter are (2.5, 2.5).

Do you need further details or have any questions about this process?

Here are some related questions you might find interesting:

  1. How do you calculate the area of a triangle using its incenter?
  2. What is the relationship between the incenter and the circumcenter of a triangle?
  3. How do you determine the area of a triangle given its side lengths?
  4. What is the importance of the incenter in geometric constructions?
  5. How do you calculate the coordinates of the centroid of a triangle?

Tip: The incenter is always equidistant from the sides of the triangle, as it lies on the angle bisectors.

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Math Problem Analysis

Mathematical Concepts

Geometry
Triangles
Incenter
Distance Formula

Formulas

Incenter formula: I(x, y) = ((aA_x + bB_x + cC_x) / (a + b + c), (aA_y + bB_y + cC_y) / (a + b + c))
Distance formula: Distance = √((x2 - x1)^2 + (y2 - y1)^2)

Theorems

Incenter Theorem

Suitable Grade Level

Grades 9-12