Isosceles and Equilateral Triangles

Learn and apply isosceles and equilateral triangles.

Lesson 3 of 53 parts Practice Flashcards

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Base Angles

Objective: Apply base angles in triangle problems.

The base angles of an isosceles triangle are congruent.

Worked examples

Try itAn isosceles triangle has a vertex angle of 34°. Find each base angle.Show answer

73°. The base angles match and share the remaining 180°−vertex angle.

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Objective: Apply base angles in triangle problems.

The base angles of an isosceles triangle are congruent.

Worked examples

Try itAn isosceles triangle has a vertex angle of 34°. Find each base angle.Show answer

73°. The base angles match and share the remaining 180°−vertex angle.

Objective: Apply converse base angles in triangle problems.

If two angles of a triangle are congruent, their opposite sides are congruent.

Worked examples

Try itTwo angles in triangle T1 are both 31°. What must be true?Show answer

Their opposite sides are congruent.. Converse Base Angles Theorem: congruent angles face congruent sides.

Objective: Apply equilateral triangles in triangle problems.

An equilateral triangle has three congruent sides and three 60° angles.

Worked examples

Try itEquilateral triangle E1 has side length 5. What is each interior angle?Show answer

60°. All three angles are equal and sum to 180°, so each is 60°.

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