We are given a quadrilateral with two right angles, one angle of $130^\circ$, and two equal sides in the triangle portion of the quadrilateral. Our goal is to find the measure of angle $k$.

GeometryQuadrilateralTriangleAnglesIsosceles TriangleAngle SumGeometric Proof
2025/6/3

1. Problem Description

We are given a quadrilateral with two right angles, one angle of 130130^\circ, and two equal sides in the triangle portion of the quadrilateral. Our goal is to find the measure of angle kk.

2. Solution Steps

First, let's analyze the quadrilateral. The sum of the interior angles of a quadrilateral is 360360^\circ. Let's call the top left angle of the quadrilateral xx. The other angles are 9090^\circ, 9090^\circ, and 130130^\circ. So we have
x+90+90+130=360x + 90^\circ + 90^\circ + 130^\circ = 360^\circ.
x+310=360x + 310^\circ = 360^\circ.
x=360310x = 360^\circ - 310^\circ.
x=50x = 50^\circ.
Now consider the triangle. We are given that two of its sides are equal, which means it is an isosceles triangle. Therefore, the angles opposite those sides are also equal. Let's call these angles kk.
The sum of the angles in a triangle is 180180^\circ. We know that the top angle of the triangle is x=50x=50^\circ.
Therefore, k+k+50=180k + k + 50^\circ = 180^\circ.
2k+50=1802k + 50^\circ = 180^\circ.
2k=180502k = 180^\circ - 50^\circ.
2k=1302k = 130^\circ.
k=1302k = \frac{130^\circ}{2}.
k=65k = 65^\circ.

3. Final Answer

k=65k = 65^\circ

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