Interpret parameters, constants, and input–output pairs in context. | Nonlinear functions | SAT Math

Explaining what numbers and variables in an equation mean within the real-world situation described.

核心知识

Every constant, coefficient, and variable in a model has a real-world meaning tied to the scenario. The SAT asks you to match a specific number in the equation to what it represents — an initial value, a rate of change, a maximum, a time, etc.

深入理解

These questions give you a formula and a context, then ask "What does the 500 represent?" or "What is the meaning of the vertex?"

Start by identifying what the input and output variables represent. If $𝑃 (𝑡) = 500 (1.04) 𝑡$ models a population after $𝑡$ years:

$𝑡$ is time in years.
$𝑃 (𝑡)$ is the population.
500 is the population when $𝑡 = 0$ — the initial population.
1.04 is the yearly growth factor, meaning a 4% annual increase.

For quadratics like $ℎ (𝑡) = - 16 𝑡 2 + 48 𝑡 + 5$ :

5 is $ℎ (0)$ , the initial height.
The coefficient $- 16$ relates to gravitational acceleration.
The vertex y-value is the maximum height.

The most reliable approach: substitute a simple value (often 0 or 1) and see what the equation gives you. This grounds abstract symbols in concrete meaning.

分步讲解

Identify input and output: what does the independent variable measure? What does the function value measure?
Plug in $𝑥 = 0$ (or $𝑡 = 0$ ) to interpret the constant term / initial value.
Look at the base or coefficient to interpret rates, factors, or slopes.
Match the specific number the question asks about to its role in the equation.

常见误解

Confusing the growth factor with the growth rate: in $1.04 𝑡$ , the factor is 1.04 but the rate is 4%, not 104%.
Interpreting the coefficient $𝑎$ in a quadratic as a rate of change — it controls the curvature, not a constant rate.
Misidentifying which variable is input and which is output, especially when the equation uses non-standard letters.

题目

示例解析

A store's weekly revenue, in dollars, is modeled by $𝑅 (𝑥) = - 2 𝑥 2 + 80 𝑥 + 150$ , where $𝑥$ is the number of units sold. What does the 150 represent in this model?

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