Math Problem Statement

In a right-angled triangle ABC with ∠B = 90°, AB = 8 units and BC = 6 units. Point D is on side AC such that AD:DC = 2:3. Point E is on side BC such that BE:EC = 3:4. If the area of triangle BDE is maximized, what is the ratio of the areas of triangles BDE and ABC?

Solution

To solve this problem, let’s break it down step-by-step.

Step 1: Understanding the triangle dimensions

In the right-angled triangle ABCABC with B=90\angle B = 90^\circ, we have:

  • AB=8AB = 8 units
  • BC=6BC = 6 units

Using the Pythagorean theorem, we can calculate ACAC, the hypotenuse: AC=AB2+BC2=82+62=64+36=100=10 unitsAC = \sqrt{AB^2 + BC^2} = \sqrt{8^2 + 6^2} = \sqrt{64 + 36} = \sqrt{100} = 10 \text{ units}

Step 2: Determining the coordinates of points AA, BB, and CC

To make calculations easier, let’s assign coordinates to points:

  • Let BB be at the origin: B=(0,0)B = (0, 0)
  • AA will be along the vertical axis, so A=(0,8)A = (0, 8)
  • CC will be along the horizontal axis, so C=(6,0)C = (6, 0)

Step 3: Finding the coordinates of point DD

Point DD is on side ACAC such that AD:DC=2:3AD:DC = 2:3. This means DD divides ACAC in the ratio 2:32:3.

Using the section formula for a point dividing a line segment in a given ratio (m:n)(m:n): D=(mx2+nx1m+n,my2+ny1m+n)D = \left(\frac{m \cdot x_2 + n \cdot x_1}{m + n}, \frac{m \cdot y_2 + n \cdot y_1}{m + n}\right) Substitute A=(0,8)A = (0, 8), C=(6,0)C = (6, 0), m=2m = 2, and n=3n = 3: D=(26+302+3,20+382+3)=(125,245)=(2.4,4.8)D = \left(\frac{2 \cdot 6 + 3 \cdot 0}{2 + 3}, \frac{2 \cdot 0 + 3 \cdot 8}{2 + 3}\right) = \left(\frac{12}{5}, \frac{24}{5}\right) = \left(2.4, 4.8\right)

Step 4: Finding the coordinates of point EE

Point EE is on side BCBC such that BE:EC=3:4BE:EC = 3:4. This means EE divides BCBC in the ratio 3:43:4.

Using the section formula again: E=(36+403+4,30+403+4)=(187,07)=(2.571,0)E = \left(\frac{3 \cdot 6 + 4 \cdot 0}{3 + 4}, \frac{3 \cdot 0 + 4 \cdot 0}{3 + 4}\right) = \left(\frac{18}{7}, \frac{0}{7}\right) = \left(2.571, 0\right)

Step 5: Calculating the area of ABC\triangle ABC

The area of ABC\triangle ABC can be calculated using the formula: Area of ABC=12×AB×BC=12×8×6=24 square units\text{Area of } \triangle ABC = \frac{1}{2} \times AB \times BC = \frac{1}{2} \times 8 \times 6 = 24 \text{ square units}

Step 6: Calculating the area of BDE\triangle BDE

To find the area of BDE\triangle BDE, we can use the formula for the area of a triangle given vertices (x1,y1)(x_1, y_1), (x2,y2)(x_2, y_2), and (x3,y3)(x_3, y_3): Area=12x1(y2y3)+x2(y3y1)+x3(y1y2)\text{Area} = \frac{1}{2} \left| x_1(y_2 - y_3) + x_2(y_3 - y_1) + x_3(y_1 - y_2) \right| Substituting the coordinates of BB, DD, and EE:

  • B=(0,0)B = (0, 0)
  • D=(2.4,4.8)D = \left(2.4, 4.8\right)
  • E=(2.571,0)E = \left(2.571, 0\right)

Area of BDE=120(4.80)+2.4(00)+2.571(04.8)\text{Area of } \triangle BDE = \frac{1}{2} \left| 0(4.8 - 0) + 2.4(0 - 0) + 2.571(0 - 4.8) \right| =120+02.5714.8=12×12.3088=12×12.3088=6.1544 square units= \frac{1}{2} \left| 0 + 0 - 2.571 \cdot 4.8 \right| = \frac{1}{2} \times | -12.3088 | = \frac{1}{2} \times 12.3088 = 6.1544 \text{ square units}

Step 7: Finding the ratio of areas of BDE\triangle BDE and ABC\triangle ABC

Now, we can calculate the ratio of the areas: Ratio=Area of BDEArea of ABC=6.154424=0.2564\text{Ratio} = \frac{\text{Area of } \triangle BDE}{\text{Area of } \triangle ABC} = \frac{6.1544}{24} = 0.2564 In simplest form, this ratio is approximately 14\boxed{\frac{1}{4}}.

Would you like further details or have any questions?


  1. How would the solution change if AD:DCAD:DC were a different ratio?
  2. How can the section formula be applied to find coordinates of dividing points?
  3. Why do we use absolute values when finding the area using coordinates?
  4. Can the area of triangle BDEBDE be maximized further with different segment divisions?
  5. How would the coordinates approach differ if ABC\triangle ABC were not right-angled?

Tip: In coordinate geometry, always label points and use clear steps for calculations.

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Math Problem Analysis

Mathematical Concepts

Geometry
Trigonometry
Coordinate Geometry

Formulas

Area of a triangle = (1/2) * base * height
Pythagorean theorem
Section formula for dividing segments

Theorems

Pythagorean theorem
Area calculation using vertex coordinates

Suitable Grade Level

Grades 9-12