Question

Difficulty: MediumFunction Notation and Transformations

For the function ff, selected values of xx and f(x)f(x) are shown in the table below.

xxf(x)f(x)
−1-144
1122
33−1-1
5566

The function gg is defined by g(x)=a⋅f(x−2)+5g(x) = a \cdot f(x - 2) + 5, where aa is a constant. If g(5)=3g(5) = 3, what is the value of aa?

Answer: 2

Answer

2
Evaluating g(5)g(5) using the formula g(x)=a⋅f(x−2)+5g(x) = a \cdot f(x - 2) + 5 requires finding f(5−2)=f(3)f(5 - 2) = f(3). From the table, f(3)=−1f(3) = -1. Substituting these values yields 3=a(−1)+53 = a(-1) + 5, which simplifies to −a=−2-a = -2, or a=2a = 2.

Step-by-Step Solution

1
Express g(5)g(5) using the given definition of g(x)g(x).
g(5)=a⋅f(3)+5g(5) = a \cdot f(3) + 5
By substituting x=5x = 5 into the definition g(x)=a⋅f(x−2)+5g(x) = a \cdot f(x - 2) + 5, we obtain g(5)=a⋅f(5−2)+5=a⋅f(3)+5g(5) = a \cdot f(5 - 2) + 5 = a \cdot f(3) + 5.
2
Find the value of f(3)f(3) from the table.
f(3)=−1f(3) = -1
Looking at the row where x=3x = 3 in the table, the corresponding output f(x)f(x) is −1-1.
3
Substitute the known values into the equation for g(5)g(5) and solve for aa.
a=2a = 2
Substitute g(5)=3g(5) = 3 and f(3)=−1f(3) = -1 into the equation to get 3=a(−1)+53 = a(-1) + 5. Subtracting 5 from both sides gives −2=−a-2 = -a, which simplifies to a=2a = 2.

Key Concept

Evaluating a transformed function using a table of values.
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