Math Problem Statement

A, B, C, D, and E are five points on the circumference of a circle. EB is parallel to DC, EAC = 72°, AEB = 25°, and X is the intersection of AC and EB. Find (i) angle EBC, (ii) angle CXB, and (iii) angle EDC.

Solution

Let's go through each part of the question using properties of cyclic quadrilaterals and angles in circles.

Given:

  • EAC=72EAC = 72^\circ
  • AEB=25AEB = 25^\circ
  • EBDCEB \parallel DC

We need to find:

  1. EBC\angle EBC
  2. CXB\angle CXB
  3. EDC\angle EDC

Solution:

  1. Finding EBC\angle EBC:

    Since EBDCEB \parallel DC and EAC=72EAC = 72^\circ, we can apply the alternate segment theorem. This tells us that: EBC=EAC=72\angle EBC = \angle EAC = 72^\circ

    Answer for (i): EBC=72\angle EBC = 72^\circ

  2. Finding CXB\angle CXB:

    Since AEB=25AEB = 25^\circ, this angle subtends arc ABAB in the circle. Therefore, CXB\angle CXB, which is an angle subtended by the same arc ABAB on the opposite side, is equal to AEB\angle AEB: CXB=AEB=25\angle CXB = \angle AEB = 25^\circ

    Answer for (ii): CXB=25\angle CXB = 25^\circ

  3. Finding EDC\angle EDC:

    Because EDCEDC is opposite EACEAC in the cyclic quadrilateral AEDCAEDC, we use the property that opposite angles in a cyclic quadrilateral add up to 180180^\circ: EDC=180EAC=18072=108\angle EDC = 180^\circ - \angle EAC = 180^\circ - 72^\circ = 108^\circ

    Answer for (iii): EDC=108\angle EDC = 108^\circ

Final Answers:

  1. EBC=72\angle EBC = 72^\circ
  2. CXB=25\angle CXB = 25^\circ
  3. EDC=108\angle EDC = 108^\circ

Would you like further clarification on any of these steps?


Here are some related questions to expand your understanding:

  1. Why do opposite angles in a cyclic quadrilateral add up to 180180^\circ?
  2. How can the alternate segment theorem be applied in different situations?
  3. What are the properties of angles subtended by the same arc in a circle?
  4. How would the solution change if EBEB were not parallel to DCDC?
  5. What other theorems are commonly used in cyclic quadrilateral problems?

Tip: Always look for parallel lines in cyclic quadrilateral problems; they often allow the use of the alternate segment theorem for angle calculations.

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Math Problem Analysis

Mathematical Concepts

Circle Theorems
Angles in a Circle
Cyclic Quadrilateral Properties

Formulas

Sum of opposite angles in a cyclic quadrilateral = 180°

Theorems

Alternate Segment Theorem
Angles Subtended by the Same Arc

Suitable Grade Level

Grades 9-10