Grade 6 · Math

6th grade Angles and sides of triangles worksheet

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Angles and sides of triangles

Grade 6 Math Worksheet

NameDate

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

Jun sketches a tent end, a triangle with angles of 30° and 100°. What is the size of its third angle, in degrees?
Kira sketches a boat sail, a triangle with angles of 48° and 62°. What is the size of its third angle, in degrees?
Luz sketches a kite wing, a triangle with angles of 72° and 41°. What is the size of its third angle, in degrees?
Noah sketches a sled ramp as a right triangle. One of its other angles is 38°. What is the third angle, in degrees?
Pia sketches a ladder against a wall as a right triangle. One of its other angles is 62°. What is the third angle, in degrees?
6.
Ari cuts three straws to stand in a water glass. They are 18 cm, 5 cm and 8 cm long. Can the three straws make a triangle?
- Yes: any three straws make a triangle
- No: the two shorter straws together (13 cm) are not longer than the longest (18 cm)
- No: a triangle needs all three straws the same length
7.
Bo cuts three straws to stand in a water glass. They are 12 cm, 5 cm and 7 cm long. Can the three straws make a triangle?
- No: a triangle needs all three straws the same length
- Yes: the two shorter straws reach 12 cm, as far as the longest, so they fit and a triangle forms
- No: the two shorter straws together (12 cm) are not longer than the longest (12 cm)
Read this first
Three sets of straws shown as bars on a number line in cm, ticks every 1 cm
The lengths in each set are the ones listed in the choices.
8.
Esme sorts straws into three sets next to a water glass. Which set can make a triangle?
- 6 cm, 7 cm and 10 cm
- 2 cm, 3 cm and 8 cm
- 4 cm, 5 cm and 9 cm
9.
Jun sorts straws into three sets next to a water glass. Which set can make a triangle?
- 5 cm, 6 cm and 11 cm
- 8 cm, 9 cm and 12 cm
- 3 cm, 5 cm and 13 cm
10.
Kira sorts straws into three sets next to a water glass. Which set can make a triangle?
- 7 cm, 10 cm and 14 cm
- 6 cm, 9 cm and 15 cm
- 4 cm, 5 cm and 12 cm

6th grade Angles and sides of triangles worksheet – printable — Print: 1 2 3 4 5 6

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?

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.

More grade 6 math

See all grade 6 math

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