Using ruler and compass only, draw a right angle.
Answer:
Draw a ray ^@OA^@. With ^@O^@ as the center and any convenient radius, draw an arc, cutting ^@OA^@ at ^@P^@. With ^@P^@ as the center and the same radius, draw an arc, cutting the arc drawn in step 2 at ^@Q^@. With ^@Q^@ as the center and the same radius, draw an arc, cutting the arc drawn in step 2 at ^@R^@. With ^@Q^@ as the center and the same radius, draw an arc. With ^@R^@ as the center and the same radius, draw an arc, cutting the arc drawn in the previous step at ^@B^@. Draw ^@OB^@ and produce it to ^@C^@.^@\angle AOC^@ is the angle of measure ^@90^\circ^@.