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Mathematics

In the figure, given below, AB is parallel to CD and CA = CE.

In the figure, given below, AB is parallel to CD and CA = CE. Chapterwise Revision (Stage 2), Concise Mathematics Solutions ICSE Class 9.

If angle ACE = 74° and angle EAB = 15°, find the angles AEB and BCD.

Triangles

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Answer

Given: AB // CD, CA = CE

∠ACE = 74°, ∠EAB = 15°

Since CA = CE, the angles opposite to equal sides are also equal:

∠CAE = ∠CEA = a

Using the angle sum property in Δ ACE,

⇒ ∠ACE + ∠AEC + ∠EAC = 180°

⇒ 74° + a + a = 180°

⇒ 74° + 2a = 180°

⇒ 2a = 180° - 74°

⇒ 2a = 106°

⇒ a = 106°2\dfrac{106°}{2}

⇒ a = 53°

So, ∠CAE = ∠CEA = 53°.

Since ∠CEA and ∠AEB form a linear pair,

∠CEA + ∠AEB = 180°

⇒ 53° + ∠AEB = 180°

⇒ ∠AEB = 180° - 53°

⇒ ∠AEB = 127°

In Δ AEB, using the angle sum property:

⇒ ∠AEB + ∠ABE + ∠EAB = 180°

⇒ 127° + ∠ABE + 15° = 180°

⇒ 142° + ∠ABE = 180°

⇒ ∠ABE = 180° - 142°

⇒ ∠ABE = 38°

Since AB || CD, ∠BCD = ∠ABE (corresponding angles property):

∠BCD = 38°

Hence, ∠AEB = 127° and ∠BCD = 38°.

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