Justifying Equation Steps
Aligned to A-REI.A.1 — Common Core State Standards for Mathematics.
What this lesson teaches
Every step in solving an equation is justified by a property that keeps both sides equal — adding the same amount, or multiplying by the same nonzero number. Naming the property proves the method is valid.
Worked example
Solve 3x + 2 = 14. Subtract 2 from both sides (subtraction property of equality): 3x = 12. Divide both sides by 3 (division property of equality): x = 4.
Practice questions
- Solve 5x − 7 = 18 and name the property used at each step.
- Explain why you may add 6 to both sides of x − 6 = 10.
- A student divides only one side by 2. Explain why this breaks the equality.
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
Justificar los Pasos de una Ecuación
Cada paso al resolver una ecuación se justifica con una propiedad que mantiene iguales ambos lados: sumar la misma cantidad, o multiplicar por el mismo número distinto de cero. Nombrar la propiedad prueba que el método es válido.
Ejemplo: Resuelve 3x + 2 = 14. Resta 2 en ambos lados (propiedad de resta de la igualdad): 3x = 12. Divide ambos lados entre 3 (propiedad de división de la igualdad): x = 4.
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