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Question

ABC is an equilateral triangle. Its side BC is produced upto point E such that C is mid-point of BE. Calculate the measure of angles ACE and AEC.

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Solution

We form our diagram from given information , As :

Here , AB = BC = CA as ABC is a equilateral triangle, Also given BC = CE ( As C is mid point of BE ) , Then

AB = BC = CA = CE

We know equilateral triangle all angles are at 60° .

So,

∠ ABC = ∠ ACB = ∠ BAC = 60° --- ( 1 )

And

∠ ACB + ∠ ACE = 180° , Substitute value from equation 1 we get

60° + ∠ ACE = 180°

∠ ACE = 120° --- ( 2 )

And triangle AEC is a isosceles triangle as side AC = CE so from base angle theorem we get

∠ AEC = ∠ EAC --- ( 3 )

From angle sum property of triangle we get in triangle AEC

∠ AEC + ∠ EAC + ∠ ACE = 180° , Substitute values from equation 2 and 3 and get

∠ AEC + ∠ AEC + 120° = 180°

2 ∠ AEC = 60°

∠ AEC = 30°

Therefore,

∠ ACE = 120° and ∠ AEC = 30° ( Ans)


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