The document discusses several rules regarding angles: 1) The sum of angles on a straight line is always 180 degrees. 2) The sum of angles around a point is always 360 degrees. 3) When two lines cross, opposite angles are equal. 4) The sum of angles inside a triangle is always 180 degrees. The sum of angles in any quadrilateral or polygon is always 360 degrees.

1. October 4, 2012
Angles
1. Angle facts
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2. Explanation October 4, 2012
The sum of the angles on a straight line is always 180º.
b
140º
a
40º
You can describe this rule using letters.
40 + 140 = 180
a b
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3. Explanation October 4, 2012
The sum of the angles round a point is always 360º.
a
140º
d
40º
b
40º
c
140º
You can describe this rule using letters.
140 + 40 + 140 c + d = 360
a b + + 40
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4. Explanation October 4, 2012
When two lines cross, the opposite angles are equal.
a
140º
c
40º
d
40º
b
140º
You can describe this rule using letters.
a=b c=d
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5. Explanation October 4, 2012
The sum of the angles inside a triangle is always 180º.
b
c
a
You can describe this rule using letters.
a + b + c = 180
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6. Revise October 4, 2012
These are the four types of triangle.
Right-angle
Isosceles
Scalene
Equilateral
Equal sides can be shown using a small ‘dash’.
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7. Explanation October 4, 2012
The sum of the angles in a quadrilateral is always 360º.
b
63º
69º
a
124º
d 104º
c
69 + 63 + 104 + 124 = 360
a b c d
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8. Explanation October 4, 2012
The angles in this quadrilateral still add up to 360º, even
though it is a re-entrant shape.
You can see this if you think of it as two triangles.
180 + 180 = 360
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9. Practise October 4, 2012
Find the missing angles.
144º 65º
85º
c
88º
144º
a 132º
46º
b
78º
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End