40-40 isosceles triangle

Geometry Level 3

How many different triangles are there, which satisfy the following properties:

  1. The triangle is isosceles.
  2. The triangle has an angle which is 4 0 40 ^ \circ .
  3. The triangle has a side of length 40.

Details and assumptions

2 triangles are different if they are not congruent.
Rotations, reflections and translations of a triangle are considered the same.


The answer is 4.

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1 solution

Arron Kau Staff
May 13, 2014

From the first and second conditions, the triangle must either be 4 0 4 0 10 0 40^\circ - 40^ \circ - 100^ \circ or 4 0 7 0 7 0 40^\circ - 70^ \circ - 70^ \circ .

To satisfy the third condition, either the equal sides, or the base of the triangle must be equal to 40. This gives 2 × 2 = 4 2 \times 2 = 4 different triangles which satisfy the conditions.

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