CCSS.Math.Content.HSA-CED.A.4
The standard
Rearrange formulas to highlight a quantity of interest, using the same reasoning as in solving equations.
Common Core State Standards for Mathematics
What this standard means
Students need to isolate one variable in a formula when the formula has several variables. They should treat the other variables like numbers, use inverse operations, keep equations balanced, and explain each step.
Mastery means students can rearrange formulas from geometry, science, and finance, not just one-step examples. They can handle variables in denominators, parentheses, squares, and coefficients. Common stuck points are dividing by a variable term, losing negative signs, and thinking a letter must have a known value before it can be moved.
Ways to teach it
- Give pairs formula cards, such as area, density, interest, and speed, and have them solve each for a different variable on whiteboards.
- Ask students to write: How is isolating r in a formula like solving 3x + 5 = 20, and how is it different?
- Use an exit ticket with two formulas, one simple and one with parentheses, and ask students to isolate the named variable.
- Use a phone plan cost formula and have students rearrange it to find the number of months from total cost, fee, and monthly charge.
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Related standards
- CCSS.Math.Content.7.EE.B.4
Use variables to represent quantities in a real-world or mathematical problem, and construct simple equations and inequalities to solve problems by reasoning ab...
- CCSS.Math.Content.HSA-SSE.B.3
Choose and produce an equivalent form of an expression to reveal and explain properties of the quantity represented by the expression.
- CCSS.Math.Content.7.EE.A.2
Understand that rewriting an expression in different forms in a problem context can shed light on the problem and how the quantities in it are related.
- CCSS.Math.Content.HSA-SSE.B
Write expressions in equivalent forms to solve problems