Lesson 4-2 - Equilateral & Isosceles Triangles

Which angle is the vertex angle? #1

• <C

• <A

• <B

Which segment is the base? #2

• Segment AB

• Segment BC

• Segment AC

Find the value of x. #3

HINT: REMEMBER THIS IS AN ISOSCELES TRIANGLE(2 CONGRUENT SIDES AND 2 CONGRUENT BASE ANGLES)

• 90

• 45

• 22

• 35

Answer explanation

Find the value of x. #4

HINT: THIS IS AN ISOSCELES TRIANGLE (2 CONGRUENT SIDES AND 2 CONGRUENT ANGLES)

• 1

• 4

• 5

• 8

Find the value of y. #5

HINT: THIS IS AN EQUILATERAL TRIANGLE (3 CONGRUENT SIDES AND 3 CONGRUENT 60 DEGREE ANGLES ANGLES)

Answer explanation

What is the measure of ∠A? #6

HINT: THIS IS AN ISOSCELES TRIANGLE (BASE ANGLES ARE CONGRUENT). CHOOSE ANGLE A TO BE X OR THE (UNKNOWN ANGLE).

• 46

• 134

• 90

• 88

Answer explanation

What is the measure of ∠T?

#7

HINT: THIS IS AN ISOSCELES TRIANGLE (BASE ANGLES ARE CONGRUENT) ANGLE S=ANLGE T. THEN USE THE TRIANGLE SUM THEOREM TO SOLVE FOR X AND PLUG X BACK INTO ANGLE T.

• 4

• 52

• 76

• 25

What is the value of y?

#8

HINT: THIS IS AN ISOSCELES TRIANGLE (BASE ANGLES ARE CONGRUENT) ANGLE M=ANLGE O. THEN USE THE TRIANGLE SUM THEOREM TO SOLVE FOR Y.

What is the measure of ∠D? #9

HINT: THIS IS AN ISOSCELES TRIANGLE (BASE ANGLES ARE CONGRUENT) ANGLE D=ANLGE E. THEN USE THE TRIANGLE SUM THEOREM TO SOLVE FOR X AND PLUG X BACK INTO ANGLE D.

If an Isosceles triangle has two BASE angles that are 76°. Then what is the measure of the vertex angle? Label unknown angle as x. #10

HINT: DRAW AND LABEL YOUR TRIANGLE AND USE THE TRIANGLE SUM THEOREM TO SOLVE FOR THE MISSING VERTEX ANGLE.