Math Problem Statement

In fig. 1.1, lines EF and GH intersect at O. If ∠GOE + ∠FOA = 80° and ∠FOH = 40°, find ∠FOA and reflex ∠GOA.

Solution

In this question, you're asked to find the measures of angles FOA\angle FOA and the reflex angle GOA\angle GOA, based on the given information. Let's break it down step by step.

Information given:

  • GOE+FOA=80\angle GOE + \angle FOA = 80^\circ
  • FOH=40\angle FOH = 40^\circ

Step 1: Understanding the Geometry

From the diagram:

  • EFEF and GHGH intersect at point OO.
  • FOH=40\angle FOH = 40^\circ is the angle formed between the lines FOFO and OHOH.
  • The sum GOE+FOA=80\angle GOE + \angle FOA = 80^\circ represents the combined angles from points GG to EE and from FF to AA.

Step 2: Calculate FOA\angle FOA

We know that angles on a straight line add up to 180180^\circ. Here, FOH\angle FOH and FOA\angle FOA lie on the same straight line FHFH, so: FOA+FOH=180\angle FOA + \angle FOH = 180^\circ Substituting FOH=40\angle FOH = 40^\circ: FOA+40=180\angle FOA + 40^\circ = 180^\circ Solving for FOA\angle FOA: FOA=18040=140\angle FOA = 180^\circ - 40^\circ = 140^\circ

Step 3: Reflex Angle GOA\angle GOA

The reflex angle GOA\angle GOA is the larger angle around the point OO, and it is calculated as: Reflex GOA=360GOA\text{Reflex } \angle GOA = 360^\circ - \angle GOA We know that GOE+FOA=80\angle GOE + \angle FOA = 80^\circ, and since FOA=140\angle FOA = 140^\circ, GOE\angle GOE must be: GOE=80140=60\angle GOE = 80^\circ - 140^\circ = -60^\circ

Would you like further clarifications? Here are 5 questions for deeper exploration:

  1. How can we calculate the angles formed by the intersection of two lines in general cases?
  2. What are the properties of reflex angles, and how do they differ from normal angles?
  3. Why is the sum of angles on a straight line always 180180^\circ?
  4. Can the result of this problem be verified geometrically using other methods?
  5. How do we calculate unknown angles when only a few angles in a geometric figure are given?

Tip: When solving angle problems involving straight lines, always remember that adjacent angles on a straight line sum up to 180180^\circ, which is often key to solving such problems.

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Math Problem Analysis

Mathematical Concepts

Geometry
Angles
Reflex Angles
Straight Line Angles

Formulas

Sum of angles on a straight line: ∠FOA + ∠FOH = 180°
Reflex angle: Reflex ∠GOA = 360° - ∠GOA

Theorems

Angles on a straight line sum to 180°
Reflex angles measure between 180° and 360°

Suitable Grade Level

Grades 8-10