Lesson Worksheet: Angle Sum of a Triangle Mathematics • 8th Grade

In this worksheet, we will practice finding a missing angle in a triangle given the two other angles.


The measures of the base angles of an isosceles triangle are (9π‘šβˆ’2𝑛)∘ and (5π‘š+2𝑛)∘, and the measure of the vertex angle is (4π‘š)∘. Find the values of π‘š and 𝑛.

  • Aπ‘š=10, 𝑛=10
  • Bπ‘š=13, 𝑛=13
  • Cπ‘š=10, 𝑛=20
  • Dπ‘š=13, 𝑛=26


Complete the sentence: The measure of a straight angle is the sum of the measures of the interior angles of a triangle.

  • Agreater than
  • Bless than
  • Cequal to


What is the sum of the measures of the two acute angles in a right-angled triangle?


Calculate the value of π‘₯.


In triangle 𝐴𝐡𝐢, π‘šβˆ π΄=78∘ and π‘šβˆ π΅=2π‘šβˆ πΆ. What is π‘šβˆ πΆ?


Find π‘šβˆ π΄π΅πΆ.


The given design is carved on a wooden board. If ∠𝐢 is a right angle, determine the values of π‘₯, 𝑦, and 𝑧.

  • Aπ‘₯=53, 𝑦=82, 𝑧=94
  • Bπ‘₯=36, 𝑦=82, 𝑧=53
  • Cπ‘₯=36, 𝑦=41, 𝑧=94
  • Dπ‘₯=53, 𝑦=41, 𝑧=53


Determine the values of π‘₯ and 𝑦.

  • Aπ‘₯=90, 𝑦=90
  • Bπ‘₯=47, 𝑦=43
  • Cπ‘₯=43, 𝑦=47
  • Dπ‘₯=137, 𝑦=133


In triangle 𝐴𝐡𝐢, π‘šβˆ π΄=54∘ and π‘šβˆ π΅=71∘. Find π‘šβˆ πΆ.


In △𝐴𝐡𝐢, π‘šβˆ π΅=2π‘šβˆ π΄=40∘. Determine π‘šβˆ πΆ.

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