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WARM UP How many sides are there in a Triangle ____________ three four Quadrilateral ___________ Pentagon _____________ five A right angle is _____° 90 An acute angle is an angle which is ______ less than 90° An obtuse angle is an angle which greater / is ____________ than 90° more A right angle is _____° 90 An acute angle is an angle which is ______ less than 90° An obtuse angle is an angle which greater / is ____________ than 90° more ANGLE PROPERTIES When two straight lines cross, the angles formed on either side are called opposite angles Opposite angles are equal a Angles along a straight line are called supplementary angles. Supplementary angles add to 180° a Angles dividing a right angle are called complementary angles Complementary angles add to 90° b b a=b a+b= 180° a + b = 90° a b ANGLE PROPERTIES EXAMPLE When two straight lines cross, the angles formed on either side are called opposite angles Opposite angles are equal Calculate the measure of the unknown angle Angles along a straight line are called supplementary angles. Supplementary angles add to 180° Angles dividing a right angle are called complementary angles Complementary angles add to 90° (a) a 73° a = 73° (b) b + 123° = 180° 123° b b = 180° - 123° b = 57° ANGLE PROPERTIES EXAMPLE When two straight lines cross, the angles formed on either side are called opposite angles Opposite angles are equal Calculate the measure of the unknown angle (c) a Angles along a straight line are called supplementary angles. Supplementary angles add to 180° 43° a + 43° = 90° a = 90° - 43° Angles dividing a right angle are called complementary angles Complementary angles add to 90° a = 47° ANGLE PROPERTIES When two straight lines cross, the angles formed on either side are called opposite angles Opposite angles are equal Angles along a straight line are called supplementary angles. Supplementary angles add to 180° Angles dividing a right angle are called complementary angles Complementary angles add to 90° The angle with the dot is XYZ NAMING ANGLES and SIDES To identify angles in polygons or angles involving parallel lines (lines that never meet), you may need to use three letters. X Y Z EXAMPLE The right angle pictured below is labelled as ABC A A side of a triangle or polygon can be identified by the two vertices on the ends of the line segment. EXAMPLE The side labelled x can be expressed B as side AB x B C C A NAMING ANGLES and SIDES 1. Use three letters to name the angle with the dot in each diagram B (a) (b) C A B C A BCA BCD D NAMING ANGLES and SIDES 2. For each diagram, use two letters to identify the side marked with the x (a) (b) D J I x x K E F DF H JK