Question

Which of the following angles (in degree) cannot be constructed using compass and ruler?

• A. 90
• B. 45
• C. 15
• D. 20

Answer 1

The correct option is D

20

${90}^0$ can be drawn by bisecting ${180}^0$, Which is a straight line. ${45}^0$ can be drawn by bisecting ${90}^0$.
${15}^0$ can be drawn by bisecting ${60}^0$ twice.
If we look at the values of angles that can be constructed by a compass they are multiples of ${15}^0$ and 20 is not a multiple of 15.
Therefore, ${20}^0$ cannot be constructed.