Subjects geometry

Triangle Angles 247Dc9

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1. **Stating the problem:** We have triangle ABC with point D on segment AC such that ADC is a straight line. Given angles: \(\angle A = 77^\circ\), \(\angle C = 35^\circ\), \(\angle D = y^\circ\), and two angles labeled \(x^\circ\) inside the triangle at vertex B. We need to find \(x\) and \(y\).\n\n2. **Key fact:** Since ADC is a straight line, \(\angle ADC = 180^\circ\).\n\n3. **Sum of angles in triangle ABC:** \(\angle A + \angle B + \angle C = 180^\circ\). Here, \(\angle B = 2x\) because there are two angles labeled \(x^\circ\) at B.\n\n4. Write the equation for triangle ABC:\n$$77^\circ + 2x + 35^\circ = 180^\circ$$\n\n5. Simplify:\n$$112^\circ + 2x = 180^\circ$$\n\n6. Solve for \(x\):\n$$2x = 180^\circ - 112^\circ$$\n$$2x = 68^\circ$$\n$$x = \frac{68^\circ}{2}$$\n$$x = 34^\circ$$\n\n7. Since ADC is a straight line, angles \(\angle BDC = y^\circ\) and \(\angle BDA = x^\circ + 35^\circ\) must sum to 180° (linear pair). But here, \(y\) is the angle at D between B and C, so:\n$$y + 77^\circ = 180^\circ$$\n\n8. Solve for \(y\):\n$$y = 180^\circ - 77^\circ$$\n$$y = 103^\circ$$\n\n**Final answers:**\n$$x = 34^\circ, \quad y = 103^\circ$$