Math Problem Statement

Find the values of x, y, a, and b from the two geometry problems with cyclic quadrilaterals and triangles inscribed in circles.

Solution

Let's solve both problems shown in the image:

Problem 1:

The first diagram involves a cyclic quadrilateral (inscribed in a circle) with the following angle measures:

  • E=80\angle E = 80^\circ
  • F=70\angle F = 70^\circ
  • G=90\angle G = 90^\circ We need to find xx and yy (the angles C\angle C and D\angle D).

Since the quadrilateral is inscribed in a circle, we know that opposite angles of a cyclic quadrilateral are supplementary. That means:

  1. E+G=180\angle E + \angle G = 180^\circ 80+90=170y=180170=1080^\circ + 90^\circ = 170^\circ \quad \Rightarrow \quad y = 180^\circ - 170^\circ = 10^\circ

  2. F+C=180\angle F + \angle C = 180^\circ 70+x=180x=11070^\circ + x = 180^\circ \quad \Rightarrow \quad x = 110^\circ

Thus, x=110x = 110^\circ and y=10y = 10^\circ.


Problem 2:

The second diagram shows a right triangle inscribed in a circle, with:

  • a\angle a^\circ
  • b\angle b^\circ
  • The third angle inside the triangle is 3232^\circ, and the right angle is at the center of the circle.

For a triangle inscribed in a circle with one angle subtended by a diameter, the angle opposite the diameter is 9090^\circ (this is a property of the semicircle). Therefore:

  1. Since the total sum of the angles in any triangle is 180180^\circ, we have: a+b+32=180a + b + 32^\circ = 180^\circ

    Since a=90a = 90^\circ (opposite the diameter): 90+b+32=180b=5890^\circ + b + 32^\circ = 180^\circ \quad \Rightarrow \quad b = 58^\circ

Thus, a=90a = 90^\circ and b=58b = 58^\circ.


Let me know if you'd like further clarifications or details! Here are 5 related questions:

  1. How do the properties of cyclic quadrilaterals help solve angle problems in circles?
  2. What are the properties of triangles inscribed in a circle?
  3. Can you find the angles of any other polygons inscribed in a circle?
  4. How would the solution change if the quadrilateral was not cyclic?
  5. How do supplementary angles relate to inscribed shapes?

Tip: In any circle problem, remember that the sum of angles around a point or inside a polygon gives useful relations!

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Math Problem Analysis

Mathematical Concepts

Geometry
Cyclic Quadrilaterals
Inscribed Angles
Circle Theorems

Formulas

Sum of angles in a triangle = 180°
Opposite angles in a cyclic quadrilateral are supplementary

Theorems

Cyclic Quadrilateral Theorem
Inscribed Angle Theorem

Suitable Grade Level

Grades 8-10