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Trigonometry/Exercise: Chasing Angles

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Video LinksEdit

The Khan Academy has video material that walks through two very similar exercises to these, which you may find easier to follow:


The Angle Game 1Edit

Worked Example 1: Missing Angle


  • In the diagram above, the two lines marked with arrows are parallel. You are given the angle of 56o and of 115o. Find the angle x.

The angle   is the same as the 56o angle, since the two lines marked with arrows are parallel and the line that crosses them must cross parallel lines at the same angle.

The angle Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "/mathoid/local/v1/":): {\displaystyle \displaystyle \beta} is 180o-115o since it and the 115o angle add up to a straight line. So it is 65o.

We can now redraw the diagram with the angles as follows:

We have a triangle with angles x, 56o and 65o.





The Angle Game 2Edit

Worked Example 2: Missing Angle in a Star


  • In the diagram above two angles are marked as 75o and one as 101o. Find the angle c.

There is an isosceles triangle with angles 75o, 75o and an unknown angle b. So





The angle 'c' is an angle in triangle Failed to parse (Conversion error. Server ("") reported: "Cannot get mml. Server problem."): {\displaystyle \displaystyle \Delta ABC} . The other two angles are 30o and 101o.



c= 49o.