Math Problem Statement

Work out the size of the ∠EBA. Given that B, C, D, and E are points on the circumference of a circle. ED = DB and DC = CB. ∠EDB = 44°. Give reasons for your answer.

Solution

The problem asks to work out the size of angle EBA\angle EBA, where BB, CC, DD, and EE are points on the circumference of a circle. We are given that:

  • ED=DBED = DB,
  • DC=CBDC = CB, and
  • EDB=44\angle EDB = 44^\circ.

Let’s go step by step to solve this problem:

  1. Isosceles Triangle EDBEDB: Since ED=DBED = DB, triangle EDBEDB is isosceles. Therefore, the base angles of this triangle are equal. Let’s denote the two equal base angles as θ\theta.

    Since the sum of angles in a triangle is 180180^\circ, we have: 2θ+44=1802\theta + 44^\circ = 180^\circ Solving for θ\theta: 2θ=18044=1362\theta = 180^\circ - 44^\circ = 136^\circ θ=1362=68\theta = \frac{136^\circ}{2} = 68^\circ

    So, BED=BDE=68\angle BED = \angle BDE = 68^\circ.

  2. Isosceles Triangle DBCDBC: Similarly, since DC=CBDC = CB, triangle DBCDBC is also isosceles. Let’s denote the base angles as α\alpha.

    The angle at DD is given as BDC=BDEEDB=6844=24\angle BDC = \angle BDE - \angle EDB = 68^\circ - 44^\circ = 24^\circ.

    Now using the triangle angle sum property: 2α+24=1802\alpha + 24^\circ = 180^\circ Solving for α\alpha: 2α=18024=1562\alpha = 180^\circ - 24^\circ = 156^\circ α=1562=78\alpha = \frac{156^\circ}{2} = 78^\circ

    So, DBC=BDC=78\angle DBC = \angle BDC = 78^\circ.

  3. Cyclic Quadrilateral ABCEABCE: Since BB, CC, DD, and EE are on the circumference, quadrilateral ABCEABCE is a cyclic quadrilateral. The opposite angles of a cyclic quadrilateral sum to 180180^\circ. Hence, we have: EBA+ECA=180\angle EBA + \angle ECA = 180^\circ We already know that ECA=78\angle ECA = 78^\circ (from step 2), so: EBA+78=180\angle EBA + 78^\circ = 180^\circ Solving for EBA\angle EBA: EBA=18078=102\angle EBA = 180^\circ - 78^\circ = 102^\circ

Thus, the size of EBA\angle EBA is 102°.

Would you like more details on any of the steps? Here are five related questions to deepen understanding:

  1. Why is a triangle with two equal sides called isosceles, and how does it affect the angles?
  2. How do we know that the sum of the angles in any triangle is always 180°?
  3. Can the properties of cyclic quadrilaterals be applied to any other geometric shape?
  4. What other properties do isosceles triangles have, apart from equal angles opposite the equal sides?
  5. How does the Circle Theorem help solve problems involving angles in circles?

Tip: Always look out for isosceles triangles in geometry problems—they often help simplify angle calculations!

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Math Problem Analysis

Mathematical Concepts

Geometry
Circle Theorems
Isosceles Triangles
Cyclic Quadrilaterals

Formulas

Sum of angles in a triangle = 180°
Sum of opposite angles in a cyclic quadrilateral = 180°

Theorems

Circle Theorems
Isosceles Triangle Theorem
Cyclic Quadrilateral Theorem

Suitable Grade Level

Grades 9-11