SOLUTION: Let N be the number of non-congruent triangles with all the following properties: A. All three sides are integers less than or equal to 15. B. The area of the triangle is an intege

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Question 1113952: Let N be the number of non-congruent triangles with all the following properties: A. All three sides are integers less than or equal to 15. B. The area of the triangle is an integer. C. At least one angle is 30°, 45°, 60°, 120°, 135°, or 150°.
Compute N.

Answer by ikleyn(52908)   (Show Source): You can put this solution on YOUR website!
.
1.  If two adjacent side lengths are integer numbers, then with the concluded angle between them of 30°,  45°,  135°  and/or  150°

    the opposite side can not have integer length due to the cosine theorem.

    It can not even have the length expressed by a rational number.


    It follows from the cosine theorem (as I just said) and from the fact that 

       cos(30°) = ,  cos(45°) = ),  cos(135°) =   and  cos(150°) = 

    are irrational numbers.


    So, it kills all the opportunities for angles  30°,  45°,  135°  and/or  150°.



2.  Regarding the angles  60°  and  120°,  such triangles also are impossible, since their area 

    (which is half the product of two adjacent side lengths by sin(60°)  or  sin(120°))

    also can not be integer,  because   sin(60°)  = sin(120°)) =  is an irrational number.

Answer. The number of triangles under the question is  0  (zero,  ZERO).


--------------
Good problem for the day of April, 1.

        April, 1 is an International Fools' day


                For further info see this Wikipedia article

          https://en.wikipedia.org/wiki/April_Fools%27_Day



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