Question 1192097
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Use the cosine law.


Find smaller interior angle "a" 


    42^2 = 68^2 + 83^2 - 2*68*83*cos(a)

    cos(a) = {{{(68^2+83^2-42^2)/(2*68*83)}}} = 0.863660524.

        a  = arccos(0.863660524) = 30.2698952  degrees.


Hence, the largest interior angle of the parallelogram is  180 - 30.2698952 = 149.73 degrees  (rounded).    <U>ANSWER</U>
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Solved.