Calculate the CAD Angle in an Isosceles Triangle with Height AD

ABC is an isosceles triangle.

AD is its height.

Calculate the size of angle CAD ∢\text{CAD} .

AAABBBCCCDDD55

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00:00 Determine angle CAD
00:03 The following is an isosceles triangle according to the given data
00:07 In an isosceles triangle, base angles are equal
00:10 The sum of angles in the triangle (ADC) equals 180
00:22 Isolate CAD
00:34 This is the solution

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1

Understand the problem

ABC is an isosceles triangle.

AD is its height.

Calculate the size of angle CAD ∢\text{CAD} .

AAABBBCCCDDD55

2

Step-by-step solution

To solve this problem, we'll apply the properties of isosceles and right triangles.

  • Step 1: Recognize that since ABC \triangle ABC is isosceles, angles BAD=CAD \angle \text{BAD} = \angle \text{CAD} , and we are given ABD=55 \angle \text{ABD} = 55^\circ .
  • Step 2: In ABD \triangle ABD , use the angle sum property for a triangle, BAD+ABD+BDA=180 \angle \text{BAD} + \angle \text{ABD} + \angle \text{BDA} = 180^\circ .
  • Step 3: Given that BDA=90 \angle \text{BDA} = 90^\circ (since AD AD is the height), calculate BAD \angle \text{BAD} .

Applying the angle sum property:
BAD+55+90=180 \angle \text{BAD} + 55^\circ + 90^\circ = 180^\circ

Simplifying, we find:
BAD=180145 \angle \text{BAD} = 180^\circ - 145^\circ
BAD=35 \angle \text{BAD} = 35^\circ

Thus, the angle CAD \angle \text{CAD} is also 35 35^\circ because ABC \triangle ABC is isosceles and BAD=CAD \angle \text{BAD} = \angle \text{CAD} .

Therefore, the solution to this problem is 35 35 .

3

Final Answer

35

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