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6th grade Angles and sides of triangles worksheet

6 printable versionsBuilding Confidence10 questions · answer keyFree · no account

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Angles and sides of triangles

Grade 6 Math Worksheet - Building Confidence

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Circle the best answer, or write your answer on the line.

  1. Bo sketches a tent flap, a triangle with angles of 40° and 75°. The three corners fit along a straight line, which is 180°. What is the third angle, in degrees?

  2. Jun sketches a castle pennant: a triangle with angles of 20° and 55°. The three corners fit along a straight line, which is 180°. What is the third angle, in degrees?

  3. Kira sketches a school roof end, a triangle with angles of 45° and 80°. The three corners fit along a straight line, which is 180°. What is the third angle, in degrees?

  4. Luz sketches a boat sail, a triangle with angles of 60° and 80°. The three corners fit along a straight line, which is 180°. What is the third angle, in degrees?

  5. Ren has glue and three craft sticks: 6 cm, 13 cm and 4 cm long. Laid end to end, the two shorter craft sticks reach 10 cm. Can the three craft sticks make a triangle?

    • No: the two shorter craft sticks together (10 cm) are not longer than the longest (13 cm)
    • No: a triangle needs all three craft sticks the same length
    • Yes: any three craft sticks make a triangle

  6. Zee has glue and three craft sticks: 10 cm, 4 cm and 6 cm long. Laid end to end, the two shorter craft sticks reach 10 cm. Can the three craft sticks make a triangle?

    • Yes: the two shorter craft sticks reach 10 cm, as far as the longest, so they fit and a triangle forms
    • No: the two shorter craft sticks together (10 cm) are not longer than the longest (10 cm)
    • No: a triangle needs all three craft sticks the same length

  7. Ari has glue and three craft sticks: 9 cm, 5 cm and 6 cm long. Laid end to end, the two shorter craft sticks reach 11 cm. Can the three craft sticks make a triangle?

    • No: the craft sticks are all different lengths
    • Yes: the two shorter craft sticks together (11 cm) are longer than the longest (9 cm)
    • No: a triangle needs two craft sticks of the same length, and these craft sticks differ in length

  8. Bo has glue and three craft sticks: 8 cm, 4 cm and 7 cm long. Laid end to end, the two shorter craft sticks reach 11 cm. Can the three craft sticks make a triangle?

    • No: a triangle needs two craft sticks of the same length, and these craft sticks differ in length
    • No: the craft sticks are all different lengths
    • Yes: the two shorter craft sticks together (11 cm) are longer than the longest (8 cm)

  9. Noah labels triangle ABC on a map. Corner A is 30°, corner B is 70° and corner C is 80°. The longest side is across from the largest angle. Which side is the longest?

    • Side CA
    • Side AB
    • Side BC

  10. Ren labels triangle ABC on a map. Corner A is 40°, corner B is 85° and corner C is 55°. The longest side is across from the largest angle. Which side is the longest?

    • Side CA
    • Side BC
    • Side AB
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6th grade Angles and sides of triangles worksheet – printable
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About this worksheet

Angles and sides of triangles. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

  • I can find the third angle of a triangle because all three angles make 180 degrees.
  • I can tell whether three lengths can make a triangle by adding the two shorter ones.
  • I can find how long or how short the third side can be when two sides are known.
  • I can find the longest side from the angles, and the largest angle from the sides, because they sit across from each other.

Standard: state-only (CCSS 4.G.A.1, 4.MD.C.5–7, 7.G.A.2 three lengths make a triangle, 8.G.A.5 angle sum)

Words to know

angle: The space between two lines that meet at a corner, measured in degrees.

degree: A unit for angles. A straight line is 180 degrees.

right angle: A square corner, 90 degrees.

isosceles triangle: A triangle with two equal sides. The angles opposite them are equal too.

base angles: The two equal angles of an isosceles triangle, next to the unequal side.

side: One of the straight edges of a triangle.

across from: The side that does not touch a corner, or the corner that does not touch a side.

flat: Sides that lie in one line with no corner, so there is no triangle.

Common mistakes

Your child used 360° as the total of a triangle's angles. 360° is a full turn. Cut the three corners off a paper triangle and fit them side by side along a ruler: they make a straight line, which is 180°.

Your child added the two angles they were given. The missing angle is what is left over when you take those two away from 180°.

Your child left the right angle out when finding the missing angle. A right triangle already uses 90° of its 180° on the square corner.

What to say

Ask: will the missing angle be bigger or smaller than the two angles put together?

Ask: which angles have you taken away from 180°?

Questions parents ask

What is the most common mistake with angles and sides of triangles?

Your child used 360° as the total of a triangle's angles. 360° is a full turn. Cut the three corners off a paper triangle and fit them side by side along a ruler: they make a straight line, which is 180°.

Are these 6th grade math worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

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