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Find x :

Find x : Isosceles Triangles, Concise Mathematics Solutions ICSE Class 9.

Triangles

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Answer

In △ ADC,

Find x : Isosceles Triangles, Concise Mathematics Solutions ICSE Class 9.

⇒ AC = AD (Given)

⇒ ∠ACD = ∠ADC = 42° (Angles opposite to equal sides are equal)

By angle sum property of triangle,

⇒ ∠ACD + ∠ADC + ∠CAD = 180°

⇒ 42° + 42° + ∠CAD = 180°

⇒ ∠CAD + 84° = 180°

⇒ ∠CAD = 180° - 84° = 96°.

Since, BCD is a straight line.

From figure,

⇒ ∠ACD + ∠ACB = 180°

⇒ 42° + ∠ACB = 180°

⇒ ∠ACB = 180° - 42° = 138°.

In △ ABC,

⇒ AC = BC (Given)

⇒ ∠ABC = ∠CAB = z (let) (Angles opposite to equal sides are equal)

By angle sum property of triangle,

⇒ ∠ABC + ∠CAB + ∠ACB = 180°

⇒ z + z + 138° = 180°

⇒ 2z + 138° = 180°

⇒ 2z = 180° - 138°

⇒ 2z = 42°

⇒ z = 42°2\dfrac{42°}{2} = 21°.

⇒ ∠ABC = ∠CAB = 21°.

Since, EAD is a straight line.

From figure,

⇒ ∠EAB + ∠CAB + ∠CAD = 180°

⇒ x + 21° + 96° = 180°

⇒ x + 117° = 180°

⇒ x = 180° - 117° = 63°.

Hence, x = 63°.

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