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In figure 3.98, seg AB is a diameter of a circle with centre O. The bisector of ∠ACB intersects the circle at point D. Prove that, seg AD ≅ seg BD. Complete the following proof by filling in the blanks.

In figure 3.98, seg AB is a diameter of a circle with centre O. The bisector of \(\angle ACB\) intersects the circle at point D. Prove that, seg AD ≅ seg BD. Complete the following proof by filling in the blanks.

Figure: C and D lie on opposite sides of diameter AB.

Proof: Draw seg OD.

\(\angle ACB\) = □ ………. angle inscribed in semicircle

\(\angle DCB\) = □ ………. CD is the bisector of \(\angle C\)

m(arc DB) = □ ………. inscribed angle theorem

\(\angle DOB\) = □ ………. definition of measure of an arc (I)

seg OA ≅ seg OB ………. □ (II)

\(\therefore\) line OD is □ of seg AB ………. From (I) and (II)

\(\therefore\) seg AD ≅ seg BD

1 answer

Answer: OD is the perpendicular bisector of AB, so D is equidistant from A and B.

Draw seg OD.

\(\angle ACB = \) \(90^\circ\) …… angle inscribed in semicircle

\(\angle DCB = \) \(45^\circ\) …… CD is the bisector of \(\angle C\)

m(arc DB) = \(90^\circ\) …… inscribed angle theorem (\(2 \times 45^\circ\))

\(\angle DOB = \) \(90^\circ\) …… definition of measure of an arc (I)

seg OA ≅ seg OB …… radii of the same circle (II)

\(\therefore\) line OD is the perpendicular bisector of seg AB …… from (I) and (II)

Every point on the perpendicular bisector of a segment is equidistant from its end points, \(\therefore\) seg AD ≅ seg BD.

Doubtly AI · 24 Oct 2026 AI-verified · Oct 2026 Report
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