Classifying Triangles & Quadrilaterals

Who am I?

100

I have three equal sides and three equal angles. All my angles are 60°.

Equilateral Triangle

200

I have one right angle and two other angles that add up to 90°.

Right Angle Triangle

300

I have two equal sides and two equal angles. Sometimes people call me a “roof shape.”

Isosceles Triangle

400

I have four equal sides, opposite sides parallel, but no right angles.

Rhombus

500

I have one pair of parallel sides. I can look like a ramp or a bridge.

Trapezium

Triangles

100

Name the following triangle:

A triangle with sides of length 5 cm, 5 cm, and 8 cm.

Isosceles Triangle

200

Name the following triangle: A triangle with angles 40°, 60°, and 80°.

Scalene Triangle

300

One angle of a triangle is 40° and another is 75°. What is the size of the third angle?

180 - 75 - 40 = 65^o

400

A triangle has two equal sides. One of the angles at the base is 35°. Find the other two angles.

180° – (35° + 35°) = 110°.

500

In a right-angled triangle, one of the other angles is three times the size of the smallest angle. Find all three angles.

Right-angled triangle → one angle = 90°.
Let the smallest angle = x.
Other acute angle = 3x.
Equation: x + 3x + 90 = 180 → 4x = 90 → x = 22.5°.

So the angles are: 22.5°, 67.5°, 90°.

Quadrilateral

100

A quadrilateral has four equal sides and four right angles. What is its name?

Square

200

A quadrilateral has two pairs of parallel sides, but no right angles. What is its name?

Parallelogram

300

The angles in a quadrilateral are 90°, 85°, and 120°. What is the size of the fourth angle?

Angle sum of quadrilateral = 360°
90 + 85 + 120 = 295
360 – 295 = 65°

400

A quadrilateral has three angles measuring 100°, 80°, and 75°. What is the size of the fourth angle?

100 + 80 + 75 = 255
360 – 255 = 105°

500

In a kite, one pair of opposite angles is 70° and 70°. Find the other two angles.

70 + 70 = 140
360 – 140 = 220
220 ÷ 2 = 110

So the angles are 70°, 70°, 110°, 110°

Angles recap

100

Two angles add up to 90°. If one angle is 25°, what is the other angle?

90 – 25 = 65°

200

Two angles are supplementary. One angle is 110°. What is the other angle?

180 – 110 = 70°

300

A straight line is split into two angles. One is 67°. Find the other.

Straight Angles → 180 – 67 = 113°

400

Two angles are complementary. One angle is 38°. What is the other angle?

Answer: 90 – 38 = 52°

500

Three angles meet at a point to create a revolution. The first is 120° and the second is 95°. What is the third angle?

Angles around a point = 360°
120 + 95 = 215
360 – 215 = 145°