Calculate the value of .
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Calculate the value of .
Remember that a straight angle is equal to 180 degrees.
Therefore, we can work out that the angle measuring 111° and angle ACB form a straight angle.
Now let's calculate angle ACB as follows:
Then we can calculate .
Remember that the sum of angles in a triangle is equal to 180 degrees, therefore:
51
a is parallel to b.
Calculate the angles shown in the diagram.
Interior angles are inside the triangle, while exterior angles are outside. The 111° shown is exterior - it's the angle formed by extending side AC beyond point C.
Because they form a linear pair - two adjacent angles on a straight line. Linear pairs always add up to 180°, so if one angle is 111°, the other must be 180° - 111° = 69°.
No! You must use the interior angles for triangle calculations. The exterior angle 111° can't be used directly in the triangle angle sum formula.
Look at the triangle vertices. Interior angles are formed by two sides of the triangle meeting at a vertex. Exterior angles are formed when you extend one side beyond the vertex.
Check your work! Angles in triangles are always positive. A negative result usually means you used an exterior angle instead of the interior angle, or made an arithmetic error.
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