Question

The diagram shows a circle with centre O.

A, B, C & D lie on the circumference of this circle.
Given that AC is a diameter of the circle and ∠DCA = 33° and ∠BCA = 31°, find the size of ∠DAB as highlighted in the diagram.

Answer 1

Hi there, here's your answer.

Given:

A circle with center O.

A, B, C and D lie on the circumference of the circle.

AC is the diameter of the circle.

∠DCA = 33° and ∠BCA = 31°

To find:

∠DAB

Solution:

Since AC is a diameter, ∠CDA and ∠CBA will be equal to 90° (Angles in a semi-circle)

Now, ∠BCD = ∠DCA + ∠BCA

∴ ∠BCD = 33° + 31° = 64°

Now, ∠BCD + ∠CDA + ∠DAB + ∠ ABC = 360° (Angle-sum property of a quadrilateral)

Substituting the values of the angles:

64° + 90° + 90° + ∠DAB = 360°

Or

244° + ∠DAB = 360°

Therefore ∠DAB = 360° - 244° = 116°

Hope it helps!