 # Geometry: Name the Triangle

In this worksheet, students work out the missing angle in a triangle in order to identify the type of triangle. Key stage:  KS 2

Curriculum topic:   Geometry: Properties of Shapes

Curriculum subtopic:   Compare Geometric Shapes

Difficulty level:   ### QUESTION 1 of 10

Remember that the interior angles of a triangle add up to 180º.

right-angled triangle has one 90º angle.

An isosceles triangle has two equal angles.

An equilateral triangle has three equal angles, each of size 60º

Example

Two of the angles in a triangle are 35º and 110º.  Which type of triangle is it?

We must first work out the third angle which will be:

180º - (35º + 110º) = 180º - 145º = 35º

So the triangle has angles 35º , 110º, 35º

Two angles are equal so it is isosceles.

Two of the angles in a triangle are  70º  and   40º

Which type of triangle is it?

scalene

right-angled

isosceles

equilateral

Two of the angles in a triangle are  50º  and   40º

Which type of triangle is it?

scalene

right-angled

isosceles

equilateral

Two of the angles in a triangle are  50º  and   80º

Which type of triangle is it?

scalene

right-angled

isosceles

equilateral

Two of the angles in a triangle are  50º  and   60º

Which type of triangle is it?

scalene

right-angled

isosceles

equilateral

Two of the angles in a triangle are  30º  and   30º

Which type of triangle is it?

scalene

right-angled

isosceles

equilateral

Two of the angles in a triangle are  60º  and   60º

Which type of triangle is it?

scalene

right-angled

isosceles

equilateral

Two of the angles in a triangle are  45º  and   45º

Which type of triangle is it?

scalene

right-angled

isosceles

equilateral

Two of the angles in a triangle are  45º  and   75º

Which type of triangle is it?

scalene

right-angled

isosceles

equilateral

Two of the angles in a triangle are  56º  and   34º

Which type of triangle is it?

scalene

right-angled

isosceles

equilateral

Two of the angles in a triangle are  23º  and   134º

Which type of triangle is it?

scalene

right-angled

isosceles

equilateral

• Question 1

Two of the angles in a triangle are  70º  and   40º

Which type of triangle is it?

isosceles
EDDIE SAYS
180 - 70 - 40 = 70 An isosceles triangles has two equal angles, which are 70 degrees in this problem.
• Question 2

Two of the angles in a triangle are  50º  and   40º

Which type of triangle is it?

right-angled
EDDIE SAYS
180 - 50 - 40 = 90 A right-angled triangle is 90 degrees.
• Question 3

Two of the angles in a triangle are  50º  and   80º

Which type of triangle is it?

isosceles
EDDIE SAYS
180 - 50 - 80 = 50 An isosceles triangle has two equal angles which are 50 degrees here.
• Question 4

Two of the angles in a triangle are  50º  and   60º

Which type of triangle is it?

scalene
EDDIE SAYS
180 - 50 - 60 = 70 A scalene triangle has three different angles.
• Question 5

Two of the angles in a triangle are  30º  and   30º

Which type of triangle is it?

isosceles
EDDIE SAYS
An isosceles triangle has two equal angles.
• Question 6

Two of the angles in a triangle are  60º  and   60º

Which type of triangle is it?

equilateral
EDDIE SAYS
An equilateral triangle has three equal angles that are all 60 degrees.
• Question 7

Two of the angles in a triangle are  45º  and   45º

Which type of triangle is it?

right-angled
EDDIE SAYS
180 - 45 - 45 = 90 A right-angled triangle has a 90 degree angle.
• Question 8

Two of the angles in a triangle are  45º  and   75º

Which type of triangle is it?

scalene
EDDIE SAYS
180 - 45 - 75 = 60 A scalene triangle has three different angles.
• Question 9

Two of the angles in a triangle are  56º  and   34º

Which type of triangle is it?

right-angled
EDDIE SAYS
180 - 56 - 34 = 90 A right-angled triangle has a 90 degree angle.
• Question 10

Two of the angles in a triangle are  23º  and   134º

Which type of triangle is it?

isosceles
EDDIE SAYS
180 - 23 - 134 = 23 An isosceles triangle has two equal angles.
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