Question

ABCD is a rectangle to show that diagonal AC as well as angle c show that {i} ABCD is a square {ii} diagonal BD bisects angle B as well as angle D
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Answer 1

(i) We are given that ABCD is a rectangle, so

∠A = ∠C

⇒ 1/2 ∠A = 1/2 ∠C

⇒ ∠DAC = ∠DCA (Given that AC bisects ∠A and ∠C)

Thus, CD = DA (Sides opposite to equal angles are also equal)

However, DA = BC and AB = CD (Opposite sides of a rectangle are equal)

Thus AB = BC = CD = DA

ABCD is a rectangle and all the sides are equal. Hence, ABCD is a square.

(ii) Let us join BD

Since ABCD is square, AB || CD and BC || AD

In ΔBCD,

BC = CD (Sides of a square are equal to each other)

∠CDB = ∠CBD (Angles opposite to equal sides are equal) ____ (1)

However, ∠CDB = ∠ABD (Alternate interior angles as AB || CD) _____ (2)

From equations (1) and (2), ∠CBD = ∠ABD

Thus, BD bisects ∠B.

Also, ∠CBD = ∠ADB (Alternate interior angles for BC || AD) ______ (3)

So, using equations (1) and (3), ∠ADB = ∠CDB

Hence, BD bisects ∠D and ∠B.