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Find k = ?

Mathematics

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Answer

20

Step-by-step solution

4 steps
  1. Find the interior angle at the top vertex.

    The exterior angle at the top vertex is 130∘130^\circ. The interior angle, let's call it α\alpha, is supplementary to this exterior angle.

    α=180∘−130∘=50∘\alpha = 180^\circ - 130^\circ = 50^\circ
  2. Identify equal angles based on the side markings.

    The double hash marks on the right side and the bottom side indicate that these two sides are equal. In an isosceles triangle, the angles opposite the equal sides are also equal. The angle opposite the right side is the bottom-left interior angle (let's call it β\beta), and the angle opposite the bottom side is the top interior angle (α\alpha).
    Therefore, β=α=50∘\beta = \alpha = 50^\circ.

  3. Find the third interior angle of the triangle.

    The sum of the interior angles in a triangle is 180∘180^\circ. Let the bottom-right interior angle be γ\gamma.

    α+β+γ=180∘\alpha + \beta + \gamma = 180^\circ 50∘+50∘+γ=180∘50^\circ + 50^\circ + \gamma = 180^\circ 100∘+γ=180∘100^\circ + \gamma = 180^\circ γ=180∘−100∘=80∘\gamma = 180^\circ - 100^\circ = 80^\circ
  4. Use the exterior angle at the bottom-right vertex to solve for kk.

    The exterior angle at the bottom-right vertex is 5k5k, and it is supplementary to the interior angle γ\gamma.

    5k+γ=180∘5k + \gamma = 180^\circ 5k+80∘=180∘5k + 80^\circ = 180^\circ 5k=180∘−80∘5k = 180^\circ - 80^\circ 5k=100∘5k = 100^\circ k=1005k = \frac{100}{5} k=20k = 20

    The value of kk is 20\boxed{20}.

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