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Mathematics

Show that the two triangles given in the following figure are congruent.

Show that the two triangles given in the following figure are congruent. Chapterwise Revision (Stage 2), Concise Mathematics Solutions ICSE Class 9.

Triangles

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Answer

Given: BD = 28 cm

BC = 16 cm

CD = BD - BC = 28 - 16 = 12 cm

In Δ CDE, using Pythagoras theorem,

Hypotenuse2 = Base2 + Height2

⇒ CE2 = CD2 + DE2

⇒ (20)2 = (12)2 + DE2

⇒ 400 = 144 + DE2

⇒ DE2 = 400 - 144

⇒ DE2 = 256

⇒ DE = 256\sqrt{256} = 16

In Δ ABC, using Pythagoras theorem,

⇒ AC2 = AB2 + BC2

= (12)2 + (16)2

= 144 + 256

= 400

⇒ AC = 400\sqrt{400} = 20 cm

So, AB = CD, BC = DE and AC = CE.

Hence, the two triangles ABC and CDE are congruent.

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