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

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