Let’s go through each triangle one by one and find the missing angle X. Remember:
the three interior angles of any triangle always add up to 180°. We’ll use that rule for every problem.
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Triangle 1 (top left)
It’s an isosceles triangle — two sides are marked equal, so two angles are equal. One angle is 36°, and the other two are both X.
So:
X + X + 36° = 180°
→ 2X = 180° - 36° = 144°
→ X = 144° ÷ 2 =
72°
✔ Answer:
72°
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Triangle 2 (top right)
Also isosceles — two sides equal → two angles equal. Top angle is 54°, bottom two are both X.
So:
X + X + 54° = 180°
→ 2X = 180° - 54° = 126°
→ X = 126° ÷ 2 =
63°
✔ Answer:
63°
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Triangle 3 (second row, left)
This is a scalene triangle — all angles different. Two angles given: 90° and 63°. Find X.
So:
X + 90° + 63° = 180°
→ X = 180° - 90° - 63° =
27°
✔ Answer:
27°
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Triangle 4 (second row, right)
Isosceles again — two sides equal → two angles equal. The two equal angles are both 62°. So:
X + 62° + 62° = 180°
→ X = 180° - 124° =
56°
✔ Answer:
56°
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Triangle 5 (third row, left)
Isosceles — two base angles equal. Each base angle is 36°. So:
X + 36° + 36° = 180°
→ X = 180° - 72° =
108°
✔ Answer:
108°
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Triangle 6 (third row, right)
Right triangle with two equal legs → it’s also isosceles. Right angle is 90°, so the other two angles are equal (both X).
So:
X + X + 90° = 180°
→ 2X = 90°
→ X = 45°
✔ Answer:
45°
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Triangle 7 (bottom left)
Right triangle — one angle is 90°, another is 47°. Find X.
So:
X + 90° + 47° = 180°
→ X = 180° - 137° =
43°
✔ Answer:
43°
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Triangle 8 (bottom right)
Equilateral triangle — all three sides equal → all three angles equal. So each angle is:
180° ÷ 3 =
60°
✔ Answer:
60°
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Final Answer:
72°, 63°, 27°, 56°, 108°, 45°, 43°, 60°
Parent Tip: Review the logic above to help your child master the concept of triangles missing angles worksheet.
