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# equilateral triangle

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Triangle DEF is equilateral. Find AE

Mar 24, 2024

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Properties of Equilateral Triangle:

Since triangle DEF is equilateral, all three sides (DE, DF, and EF) are equal in length. Additionally, all three angles are also equal to 60 degrees.

Right Triangle ACB:

Given that angle ACB = 90 degrees and CD = 5 and CE = 4, we recognize this as a Pythagorean triple (3, 4, 5). Therefore, AC = 3.

Isosceles Triangle DEC:

Since DE = DC + CE and all sides of triangle DEF are equal, triangle DEC is isosceles with DE = 9.

Dropping an Altitude from A:

Draw an altitude from point A to side DE, intersecting DE at point H. Since triangle ACB is a right triangle with a 90-degree angle at C,

line segment AH is also an altitude of triangle DEC, splitting it into two congruent right triangles (ADH and CHE).

Finding AH:

In right triangle ADH, we know the hypotenuse (AD = AC = 3) and want to find the altitude (AH).

Since angle A is a vertex of an equilateral triangle, angle HAD = 60 degrees (half of an equilateral triangle's angle).

We can use the trigonometric ratio tangent (tan) for this situation: tan(HAD) = AH/HD.

Knowing tan(60) = √3 and that HD = DE/2 (since AH bisects DE), we can set up the equation: tan(60) = √3 = AH / (DE/2)

Solving for AH: AH = √3 * (DE/2) = √3 * (9/2) = 3√3 / 2

Finding AE:

In right triangle AEH, we know the altitude (AH = 3√3 / 2) and the base (HE = CE - CH = 4 - AC = 4 - 3 = 1).

We can use the Pythagorean theorem: AE^2 = AH^2 + HE^2

Substitute the known values: AE^2 = (3√3 / 2)^2 + 1^2 = 27/4 + 1 = 31/4

Take the square root of both sides to find AE: AE = sqrt(31)/2

Therefore, the length of AE is equal to sqrt(31)/2.

Mar 25, 2024