Math Problem Statement

In the diagram, AFGB is a straight line, BCEF is a parallelogram and triangle EFG is an isosceles triangle. Find

(i) angle GFE (ii angle FEA

In the diagram, AFGB is a straight line, BCEF is a parallelogram and triangle EFG is an isosceles triangle. Find (i) angle GFE (ii) angle FEA.

Solution

Given the diagram and the information that:

  • AFGBAFGB is a straight line,
  • BCEFBCEF is a parallelogram,
  • Triangle EFGEFG is isosceles,
  • Angles AFE=40\angle AFE = 40^\circ and AEB=65\angle AEB = 65^\circ,

We need to find:

  1. GFE\angle GFE
  2. FEA\angle FEA

(i) Finding GFE\angle GFE:

Since triangle EFGEFG is isosceles, the base angles GFE\angle GFE and FEG\angle FEG are equal. Thus, let GFE=FEG=x\angle GFE = \angle FEG = x.

In a triangle, the sum of the interior angles is always 180180^\circ. Therefore, we can write the equation for triangle EFGEFG:

x+x+GEF=180x + x + \angle GEF = 180^\circ

We already know GEF=65\angle GEF = 65^\circ (given in the diagram). Substituting this into the equation:

2x+65=1802x + 65^\circ = 180^\circ

2x=180652x = 180^\circ - 65^\circ

2x=1152x = 115^\circ

x=1152=57.5x = \frac{115^\circ}{2} = 57.5^\circ

Thus, GFE=57.5\angle GFE = 57.5^\circ.

(ii) Finding FEA\angle FEA:

We are given that AFGBAFGB is a straight line, so:

AFE+GFE=180\angle AFE + \angle GFE = 180^\circ

Substituting the values we know:

40+FEA=18040^\circ + \angle FEA = 180^\circ

FEA=1804057.5=82.5\angle FEA = 180^\circ - 40^\circ - 57.5^\circ = 82.5^\circ

Thus, FEA=82.5\angle FEA = 82.5^\circ.

Summary of Results:

  1. GFE=57.5\angle GFE = 57.5^\circ
  2. FEA=82.5\angle FEA = 82.5^\circ

Would you like more details or have further questions?

Here are 5 relative questions for deeper understanding:

  1. How do we determine the angles in an isosceles triangle?
  2. Why is the sum of the interior angles of a triangle always 180180^\circ?
  3. How does the property of straight lines help in angle calculation?
  4. What other properties of parallelograms can help solve similar problems?
  5. How do angle relationships change in different types of polygons?

Tip: Always use known properties (e.g., straight lines and triangle angle sums) to break down more complex geometric shapes.

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Math Problem Analysis

Mathematical Concepts

Geometry
Angles
Triangles
Parallelograms

Formulas

Sum of interior angles of a triangle: 180°
Angles on a straight line sum to 180°
Base angles in an isosceles triangle are equal

Theorems

Sum of angles in a triangle
Angles on a straight line
Properties of isosceles triangles

Suitable Grade Level

Grades 9-12