Lesson of the Week Triangles
Triangles are plane shapes which lie in one plane.
They have area but not volume.
Shapes that have only straight sides are called polygons.
Triangles are polygons.

The sum of the angles in any triangle is 180º.

Angle A + Angle B + Angle C = 180° EQUILATERAL

All sides are equal and all angles are equal to 60º ISOSCELES *Two sides are equal

*Angles opposite the equal sides are equal

SCALENE

*No sides are equal
*All angles are different

ACUTE-ANGLED

All angles are less than 90º (acute)

RIGHT-ANGLED

One of the three angles of the triangle is a right-angle (90º) OBTUSE-ANGLED

*One of the angles of the triangle is greater than 90º (obtuse)
*The longest side is opposite the largest angle LET'S TRY IT! Using the given information, decide what type of triangle is described.
Check your answers by selecting the blank space after the question. 1. This triangle has angles of 23º, 90º and 67º: Right triangle 2. This triangle has side lengths 7, 9 and 11º: Scalene triangle 3. This triangle has angles of 59º, 66º and 55º: Acute triangle 4. This triangle has side lengths of 12, 6 and 12: Isosceles triangle 5. This triangle has angles of 45º, 100º and 35º: Obtuse triangle 6. This triangle has angles of 60º, 60º and 60º: Equilateral triangle

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Everyday GeometrySo you don't think you will ever use geometry outside of school?

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Geometry is used in many everyday occurrences.

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Lesson of the WeekTrianglesTriangles are plane shapes which lie in one plane.

They have area but

notvolume.Shapes that have only straight sides are called polygons.

Triangles are polygons.

The sum of the angles in any triangle is 180º.

Angle A + Angle B + Angle C = 180°

EQUILATERALAll sides are equal and all angles are equal to 60º

ISOSCELES*Two sides are equal

*Angles opposite the equal sides are equal

SCALENE*No sides are equal

*All angles are different

ACUTE-ANGLEDAll angles are less than 90º (acute)

RIGHT-ANGLEDOne of the three angles of the triangle is a right-angle (90º)

OBTUSE-ANGLED*One of the angles of the triangle is greater than 90º (obtuse)

*The longest side is opposite the largest angle

LET'S TRY IT!Using the given information, decide what type of triangle is described.Check your answers by selecting the blank space after the question.

1.This triangle has angles of 23º, 90º and 67º: Right triangle2.This triangle has side lengths 7, 9 and 11º: Scalene triangle3.This triangle has angles of 59º, 66º and 55º: Acute triangle4.This triangle has side lengths of 12, 6 and 12: Isosceles triangle5.This triangle has angles of 45º, 100º and 35º: Obtuse triangle6.This triangle has angles of 60º, 60º and 60º: Equilateral triangleWebquestClick Here to go to the Great Pyramid Geometry Webquest!

Additional ResourcesThe following links provide more references to further your learning!**Illuminations**

**Math is Fun**

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