Multiple choice

If chord $AOB $ is diameter of the circle and $AC = BC$, then $\angle$ $ACB$ is equal to:

  1. $30$
  2. $60$
  3. $90$
  4. $45$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The angle subtended by a diameter at any point on the circle is 90 degrees. Since ACB is an angle on the circle subtended by the diameter AB, it must be 90 degrees.

AI explanation

Since AB is the diameter of the circle and point C lies on the circumference, triangle ABC is inscribed in a semicircle. By Thales's theorem, any triangle inscribed in a semicircle where one side is the diameter is a right triangle. Therefore, the angle opposite the diameter, angle ACB, is exactly 90 degrees.

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