Evaluating Functions

Aligned to F-IF.A.2 — Common Core State Standards for Mathematics.

What this lesson teaches

To evaluate f(x) at a value, substitute that value for x and simplify. In context, f(a) = b means the input a produces the output b.

Example 1

If f(x) = 3x − 4, find f(5). Substitute: f(5) = 3(5) − 4 = 15 − 4 = 11.

Example 2

If f(x) = x² − 1, then f(a + 1) = (a+1)² − 1 = a² + 2a. Substitute the whole expression, not just the letter.

Example 3

f(x) does not mean f times x. Reading it that way turns every function problem into nonsense.

Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.

Para evaluar f(x) en un valor, sustituye ese valor por x y simplifica. En el contexto, f(a) = b significa que la entrada a produce la salida b.

Ejemplo 1: Si f(x) = 3x − 4, halla f(5). Sustituye: f(5) = 3(5) − 4 = 15 − 4 = 11.

Ejemplo 2: Si f(x) = x² − 1, entonces f(a + 1) = (a+1)² − 1 = a² + 2a. Sustituye toda la expresión, no solo la letra.

Ejemplo 3: f(x) no significa f por x. Leerlo así convierte cada problema de funciones en un sinsentido.

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