7th Class Mathematics The Triangle and its Properties Question Bank Triangles

  • question_answer
    If one angle is the average of the other two angles and the difference between the greatest and least angles is \[{{60}^{o}},\] which triangle is formed?                    

    A)  An isosceles triangle.

    B)  An equilateral triangle.

    C)  A right angled triangle.  

    D)  A right angled isosceles triangle.

    Correct Answer: C

    Solution :

       Let the least angle be \[{{x}^{o}}\]. The greatest angle \[={{x}^{o}}+{{60}^{o}}\] Third angle \[=\frac{x+x+{{60}^{o}}}{2}=x+{{30}^{o}}\] We have, \[x+x+{{30}^{o}}+x+{{60}^{o}}={{180}^{o}}\] \[\Rightarrow \] \[3x+{{90}^{o}}={{180}^{o}}\,\,\Rightarrow \,\,x={{30}^{o}}\] \[\therefore \]The angles are \[{{30}^{o}},{{60}^{o}}\] and \[{{90}^{o}}\]. Since one of the angles is \[{{90}^{o}}\], the triangle formed is a right angled triangle.


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