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    Hello i need help with this question please

    area of triangle ABC is 21cm^2

    Calculate the size of the obtuse angle ABC. The measurements are rounded to 1DP.

    The two sides - base is 10.2cm and the height is 4.6 cm.

    thanks
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    Why are you doing maths at 1am? Go to sleep

    Since I can't sleep either...

    \frac{1}{2}ab\sin{C} = 21. What can you do with that? (Bearing in mind that you need a bit more information in order to calculate the angle.)
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    (Original post by Sonechka)
    Why are you doing maths at 1am? Go to sleep

    Since I can't sleep either...

    \frac{1}{2}ab\sin{C} = 21. What can you do with that? (Bearing in mind that you need a bit more information in order to calculate the angle.)
    I slept most of the day lol.

    I rearranged it to give 21=23.46 (simplified) x sinC

    then 21/23.46 = sin C

    C = sin-1 (21/23.46)

    C = 63.53

    but thats not what the answers say, what have i done wrong please
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    half 1 is the best time to do maths lmao
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    (Original post by wahedi01)
    I slept most of the day lol.

    I rearranged it to give 21=23.46 (simplified) x sinC

    then 21/23.46 = sin C

    C = sin-1 (21/23.46)

    C = 63.53

    but thats not what the answers say, what have i done wrong please
    You seem to have found the wrong angle; the question is asking for the obtuse angle. A diagram would definitely help.
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    You need to find half of the length to find the side length of another. Use Pythagoras' Theorem to use the height and half the base length of the triangle, to calculate another side. Then, put everything you have into the Cosine Rule. Make the angle the subject and job done.
 
 
 
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