Algebra - PSAT Math

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Question

Let f(x) be defined as follows:

f(x)=\left\{\begin{matrix} 2x-3, &x<1 & \ 4-x^2, &1\leq x< 3 & \ |4x-9|, &x\geq 3 & \end{matrix}\right.

What is the value of f(1)+f(3)+f(5)?

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Answer

The function f(x) is a piecewise function, which means that it is comprised of separate functions that change depending on the value of x. According to the problem, whenever x is less than 1, f(x) is defined by 2_x_ - 3. Whenever x is greater than or equal to one and less than 3, f(x) is defined as 4-x^2. And whenever x is greater than or equal to 3, f(x) is equal to |4_x_ – 9|.

The question asks us to find f(1) + f(3) + f(5). We need to calculate the values of f(1), f(3), and f(5) individually and then find their sum.

To find f(1), we must first decide which of the three possible functions for f(x) to use. Since f(1) means we are finding the value of f(x) when x = 1, we will have to use the second piece, which says that f(x) = 4-x^2. We can't use the function 2_x_ - 3, because this is only valid when x < 1, not when x = 1.

f(1)=4-(1)^2=4-1 = 3

Next, we will find f(3). We need to use the third piece of the function which states that f(x) = |4_x_ – 9|. Since f(3) means we are finding f(x) when x = 3, we can only use the third piece. The second piece, 4-x^2, is only defined if x is less than 3 and greater than or equal to 1.

f(3)=|4x-9|=|4(3)-9|=|12-9|=|3|=3

Lastly, we must find f(5). Again, we will use the function f(x) = |4_x_ – 9|, because when x = 5, x must be greater than 3.

f(5)=|4(5)-9|=|20-9|=|11|=11

We can now add up f(1), f(3), and f(5), which would give us 3 + 3 + 11 = 17.

The answer is 17.

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