Angle Relationships & Equations
Aligned to 7.G.B.5 — Common Core State Standards for Mathematics.
What this lesson teaches
Complementary angles add to 90°; supplementary angles add to 180°. Vertical angles (opposite each other where two lines cross) are equal. Use these facts to write an equation and solve for an unknown angle.
Worked example
Angles A and B are supplementary, with A = 2x and B = x. Then 2x + x = 180, so 3x = 180 and x = 60. Therefore A = 120° and B = 60°.
Practice questions
- Two complementary angles measure x and 3x. Find both angles.
- One of two vertical angles measures 47°. What is the other?
- Two angles on a straight line measure 5x and 4x. Solve for x, then find each angle.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Relaciones entre Ángulos y Ecuaciones
Los ángulos complementarios suman 90°; los suplementarios suman 180°. Los ángulos opuestos por el vértice (donde se cruzan dos rectas) son iguales. Usa estos hechos para plantear una ecuación y hallar un ángulo desconocido.
Ejemplo: Los ángulos A y B son suplementarios, con A = 2x y B = x. Entonces 2x + x = 180, así que 3x = 180 y x = 60. Por lo tanto A = 120° y B = 60°.
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