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? asked in Science & MathematicsMathematics · 8 years ago

Trigonometry problem, calculating internal angles of a polygon?

It is a polygon with four sides. I got the 4 lengths and one angle. Here it goes:

"Calculate the angle at A and C, knowing that the angle at B=90º and the angle at D, which is opposed to B, is obtuse (D>90º). AB=423, AD=160, BC= 162 and CD=420"

So, how do you do this?

I've already calculated angle at D, using the law of cosines. D=91.4º

1 Answer

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  • ignoramus
    Lv 7
    8 years ago
    Favorite Answer

    So you have calculated the length of the diagonal AC ?

    Then you can use the cosine rule again to find the angles DAC and CAB, which you can add together to give the angle DAB.

    You then know 3 of the angles. Subtract the sum from 360º to get the 4th.

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