Angles

When dealing with angles it’s important to see the bigger picture – that is, angles are parts of a whole, and that whole is 360 degrees.

Let's look at types of angles and what they look like.

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Important tips to remember when dealing with angles are:

• Right angle – lines that intersect are perpendicular. A little square represents a right angle.
• Straight angle – Angle in a straight line and is 180 degrees (2 sides of the straight line add to 360 degrees).
• Angles around a point add up to 360 degrees.
• Angles in a square add up to 360 degrees.
• Angles in a triangle add up to 180 degrees.
• Complementary angles are angles that together add up to 90°.
• Supplementary angles are angles that together add up to 180°.

Parallel Lines

Interestingly, there are some rules with angles when parallel lines cross. These are:

• Corresponding angles are equal (for examples, a = e).
• Alternate interior angles are equal (d = f).
• Same side interior angles add to 180° if on a straight line.

Example Question/s

Watch video for explanation of the following question/s:

In the figure below what is the value of x?

A 25° B 45° C 30° D 90°

Find the value of angle y in the figure below.

A 110° B 50° C 70° D 30°

a° = ?

A 75° B 70° C 105° D 110°

x° = ?

A 90° B 45° C 135° D 180°

Key Rules to remember

• Know the names of angles and that complementary angles add up to 90° while supplementary angles add up to 180°.
• The little square represents a right angle (90°).
• Internal angles of a triangle add up to 180° while internal angles of a square or rectangle add up to 360°.
• Know the rules with parallel lines.

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