Area of triangle = 1/2absinC

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Presentation transcript:

Area of triangle = 1/2absinC Area of Triangles A B C a b The area of a triangle can be found from two sides and the angle between them. Area of triangle = 1/2absinC Also Area of triangle = 1/2acsinB Area of triangle = 1/2bcsinA

Ex1 Ex2 A B C 4cm 2.5cm Area of triangle = 1/2absinC 70° Area of triangle = 1/2absinC = 0.5 X 4 X 2.5 x sin70° = 4.7cm2 Ex2 K L M 30m 35m 130° Area of triangle = 1/2kmsinL = 0.5 X 30 X 35 x sin130° = 402m2

Find the area of this parallelogram. Ex3 Find the area of this parallelogram. P Area  = 1/2pqsinR 22cm = 0.5 X 11 X 22 X sin66° = 110.5cm2 66° R Q 11cm So area of parallelogram = 2 X 110.5 = 221cm2

Ex4 Find the area of this quadrilateral. 15cm 14cm 15cm 76.6° 76.6° 14cm Area = 0.5 X 14 X 15 x sin76.6° = 102cm2 20cm 21cm 52° 20cm 21cm 52° Area = 0.5 X 20 X 21 x sin52° Total area = 267cm2 = 165cm2

If A + B = 180 then sinA° = sinB° Obtuse Angles A B A+B sinA° sinB° 20 160 180 0.342 0.342 35 145 180 0.574 0.574 70 110 180 0.940 0.940 43 137 180 0.682 0.682 CONCLUSION If A + B = 180 then sinA° = sinB° Ex4 sinx° = 0.643 so x = sin-10.643 = 40° or 140°