MATHS -- GEOMETRY
acute angles : sharp and pointy angles which are less than 90`
obtuse angles : wider angles (between 90` and 180`)
right angles : square corners(90`)
DRAWING ANGLES WITH A PROTRACTER :
1. Draw a base line
2.if the angle is an acute angle then you can make sure the protractor's 0 is facing inwards.
3. if it is a small angle use the outside scale.
MATHS -- GEOMETRY (2)
1. Angles in a triangle = 180' -- a+b+c=180'
2. Angles on a straight line add upto 180`-- a+b+c=180'
3. Angles in a quadrilateral add up to 360' -- a+b+c+d=360'
4. Angles round a point = 360'
5.Exterior angle of a triangle = sum of opposite interior angles. a+b=d
6. Isosceles triangles have 2 sides the same and 2 angles the same .
MATHS -- GEOMETRY (3)
Alternate angles: alternate angles are the same they are found in a Z shape.
Vertically opposite angles : vertically opposite angles add up to 180' they are found in a C or U shape
Corresponding Angles: corresponding angles are the same.They are found in an F shape.
Example ; find the angle x
There is a corresponding angle that is 115' what is x ?
Its the same !
MATHS -- GEOMETRY (4)
INTERIOR AND EXTERIOR ANGLES
For any polygon (regular or irregular)
sum of exterior angles =360'
interior angles =180' - exterior angles
for regular polygons only : exterior angles = 360/n (number of sides)
SUM OF INTERIOR ANGLES
the formula for all polygons: SUM OF ANGLES= (n-2x180')
E.G For a pentagon. pentagon = 5 sides
Sum of interior angles=(5-2)x180'=540'
MATHS -- GEOMETRY
REVISON SUMMARY QUESTIONS:
1. Give an example of an acute angle, obtuse and reflex angle (3)
2. What do the angles in a quadrilateral equal to? (1)
3. What type of angles do you find a Z shape on parallel lines? (1)
4.Work out the size of an exterior angle and an interior angle of a regular decagon (10 sided shape) (2)
5.What is the sum of the interior angles in a hexagon and heptagon (2)