# Y7MA4_Calculating angles_11_01_2012

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Category: Education

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## Presentation Transcript

### Calculating angles :

Calculating angles Lesson objective: To be able: to calculate the size of angles [Level 5/6] Key words: unknown angles Starter: Draw an angle of: 90° 180° 360°

### Slide 2:

a=30° i. How many degrees is this angle? ii. Now the angle a is 30 degrees. b How many degrees is in the angle b? 90° b = 90° - 30° = 60° Example…

### Slide 3:

a=50° i. How many degrees is this angle? ii. Now the angle a is 50 degrees. b How many degrees is in the angle b? 180° 180° - 50° = 130° Example…

### Slide 4:

Angles around a point add up to 360° α= 360° - 280° = 80° 150° + 130° = 280°

### Slide 5:

Examples… Calculate the size of each unknown angle. 110° + 120° = 230° Angles around a point add up to 360°, therefore: α = 360° - 230° = 130° 102° + 98° + 75° = 275° c = 360° - 275° = 85° c = 85°

### Slide 6:

Angles on a straight line add up to 180° b = 180° - 155° = 25°

### Slide 7:

Examples… Calculate the size of each unknown angle. α = 180° - 130° = 50° The sum of all angles on a straight line is 180°, therefore: α = 50° 75° + 25° = 100° c = 180° - 80° = 100° c = 100°

### Slide 8:

The angles in a triangle add up to 180 °. 70° + 30° = 100° 180° - 100° = 180°

### Slide 9:

Examples… Calculate the size of each unknown angle. 40° + 55° = 95° The angles in a triangle add up to is 180°, therefore: α = 180° - 95° = 85° 35° + 90° = 125° c = 180° - 125° = 55° c = 55°

### Slide 10:

When two lines intersect, the opposite angles are equal. a = d b = c d = 140° (opposite angles) e =180°-40°= 40° (angles on a straight line)

### Slide 11:

Examples… Calculate the size of each unknown angle. When two lines intersect, the opposite angles are equal, therefore: α = 50° c = 25°

Work in pairs…

Work in pairs…

More difficult..

### Slide 15:

The sum of all angles on a straight line is Angles around a point add up to The angles in a triangle add up to When two lines intersect, the opposite angles are 180°. 360°. 180 °. equal. PLENARY...