Area pf a triangle ! ?

in triangle .ABC , angleA=120 , b=10 c=18 ; what's the area ?

options:

52

78

90

156

3 Answers

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  • Anonymous
    9 years ago
    Favorite Answer

    You are given two sides b and c and an included angle A, so we can use:

    A = (1/2)bc*sin(A).

    Therefore, the area of the triangle is:

    A = (1/2)(10)(18)sin(120°) ≈ 78 square units.

    I hope this helps!

  • 9 years ago

    if you know the size of an angle and the values of the two adjacent sides you can use the sine formula for area

    A = 1/2 ab sinC where C is the angle, and a and b are the adjacent sides

    in this case

    A = 1/2 * 10 * 18 *sin 120

    = 90sin120

    =90* √3/2

    = 45√3 or 78 units squared

  • 9 years ago

    You can use the law of cosines

    a^2 = b^2 +c^2 - 2bc*cos(A)

    a^2 = (10)^2 +(18)^2 - 2(10)(18)*cos(120)

    a^2 = 604

    a = 24.58

    AREA = 77.94229666245037 Square Units

    So the answer is 78. ;)

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