The Area of a Triangle A C B

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34: A Trig Formula for the Area of a Triangle

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Presentation transcript:

The Area of a Triangle A C B How do we calculate the area of triangle ABC? The base and height in the above formula must be at right angles (or perpendicular). But we will not always know a perpendicular height. In this case there is a second formula we can use: Area = ½absinC

Example 1 Find the area of this field in hectares. Area = ½absinC 413m 68 = ½  413  234  sin68 = 44802·45m2 = 4·48ha Remember 1 hectare = 100m 10 000m2 10 000m2

Example 2 P Q R Find the area of PQR, if P = 56°, q = 23·6m and r = 43·6m. 23·6m 43·6m 56 Draw a diagram first. Label diagram. Area = ½qrsinP = ½  23·6  43·6  sin56 = 426·52m2

Today’s work Exercise 6C Pg 180 #1ad, 2, 3