Sum

In the following figure, AE = EF = AF = BE = CF = a, AT ⊥ BC. Show that AB = AC = `sqrt3xxa`

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#### Solution

Given: AE = EF = AF = BE = CF,

AT ⊥ EF

ΔAEF is equilateral triangle.

ET = TF =a/2

BT = CT = a +a/2....(1)

In right triangles, ΔATB and ΔATC,

AT = AT … (Side common to both triangles)

∠ATB = ∠ATC … (Right angles)

BT = CT …. (from 1)

∴ ΔATB ≅ ΔATC …..(by SAS)

∴ AB = AC

In ΔAEF, AE = AF = EF …(Given)

∴ ΔAEF is an equilateral triangle.

`AT =sqrt(3)/2 a` ...(Altitude of equilateral triangle)

`In ΔATB, (AB)^2=(AT)^2+(BT)^2`

`(AB)^2=(sqrt(3)/2a)2+(a+a/2)^2=(3a^2)/4+(9a^2)/4=(12a^2)/4=3a^2`

`AB=sqrt(3)a`

`i.e.,AB = AC =sqrt(3)a`

Concept: Similarity in Right Angled Triangles

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