Triangle Classification Warmup
Triangle Classification Warm-Up
Name:
Date:
Locate each triangle in the figure, then classify by sides & angles.
Classification Bank:
Sides: Equilateral • Isosceles • Scalene
Angles: Acute • Right • Obtuse • Equiangular
#1 Figure A
45° 45° 8 cm 6 cm 7 cm A B D C
a. ΔABD:
Sides:
Angles:
b. ΔACD:
Sides:
Angles:
#2 Figure B
60° 60° 120° P Q R S
a. ΔPQR:
Sides:
Angles:
b. ΔPRS:
Sides:
Angles:
#3 Figure C
64° 64° 52° 12 cm 5 cm 13 cm W Z X Y V
a. ΔWXZ:
Sides:
Angles:
b. ΔXYV:
Sides:
Angles:
#4 Figure D
135° 42° 55° 83° 7 cm 10 cm 14 cm 15 cm 12 cm K L M N
a. ΔKLM:
Sides:
Angles:
b. ΔKNM:
Sides:
Angles:
Triangle Classification Answer Key
Triangle Classification Answer Key
Teacher Key
Reference Classifications:
Sides: Equilateral • Isosceles • Scalene
Angles: Acute • Right • Obtuse • Equiangular
#1 Figure A Shared AD
45° 45° 8 cm 6 cm 7 cm A B D C
a. ΔABD: Sides: Scalene | Angles: Right
Evidence: Sides are 6, 7, 8 cm (all different); 90° angle at D.
b. ΔACD: Sides: Isosceles | Angles: Right
Evidence: AD ≅ CD by tick marks (7 cm each); angles 45°-45°-90°.
#2 Figure B Shared PR
60° 60° 120° P Q R S
a. ΔPQR: Sides: Equilateral | Angles: Equiangular
Evidence: All 3 sides tick-marked congruent; three 60° angles.
b. ΔPRS: Sides: Isosceles | Angles: Obtuse
Evidence: PR ≅ RS by tick marks; obtuse angle ∠PRS = 120° (> 90°).
#3 Figure C Shared X
64° 64° 52° 12 cm 5 cm 13 cm W Z X Y V
a. ΔWXZ: Sides: Isosceles | Angles: Acute
Evidence: WX ≅ ZX by tick marks; angles 64°, 64°, 52° (all < 90°).
b. ΔXYV: Sides: Scalene | Angles: Right
Evidence: Sides are 5, 12, 13 cm (all different); 90° right square at V.
#4 Figure D Shared KM
135° 42° 55° 83° 7 cm 10 cm 14 cm 15 cm 12 cm K L M N
a. ΔKLM: Sides: Scalene | Angles: Obtuse
Evidence: Sides are 7, 10, 14 cm (all different); obtuse angle ∠KLM = 135°.
b. ΔKNM: Sides: Scalene | Angles: Acute
Evidence: Sides are 14, 15, 12 cm (all different); angles 42°, 55°, 83° (< 90°).
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Teaching Tip: Shared segments (AD, PR, KM) belong to both adjacent triangles. Congruence tick marks establish equal side lengths without numeric values.