Evaluating functions at a value Practice Questions (Grade 9)

Question 1easy

The function $f$ is defined by $f(x) = -2x + 15$ . What is the value of $f(x)$ when $x = 3$ ?

Substitute $x = 3$ : $f(3) = -2(3) + 15 = -6 + 15 = 9$ .

Question 2easy

The function $f$ is defined by $f(x) = 5x - 7$ . What is the value of $f(x)$ when $x = 2$ ?

Substitute $x = 2$ : $f(2) = 5(2) - 7 = 10 - 7 = 3$ .

Question 3easy

The function $f$ is defined by $f(x) = x^2 + 3$ . What is the value of $f(x)$ when $x = 4$ ?

Substitute $x = 4$ : $f(4) = 4^2 + 3 = 16 + 3 = 19$ .

Question 4easy

The function $f$ is defined by $f(x) = x^2 - 5$ . What is the value of $f(x)$ when $x = 3$ ?

Substitute $x = 3$ : $f(3) = 3^2 - 5 = 9 - 5 = 4$ .

Question 5easy

The function $f$ is defined by $f(x) = \sqrt{x + 5}$ . What is the value of $f(x)$ when $x = 11$ ?

Substitute $x = 11$ : $f(11) = \sqrt{11 + 5} = \sqrt{16} = 4$ .

Question 6easy

The function $f$ is defined by $f(x) = \sqrt{2x + 1}$ . What is the value of $f(x)$ when $x = 4$ ?

Substitute $x = 4$ : $f(4) = \sqrt{2(4) + 1} = \sqrt{9} = 3$ .

Question 7easy

The function $f$ is defined by $f(x) = \dfrac{x}{2} + 6$ . What is the value of $f(x)$ when $x = 4$ ?

Substitute $x = 4$ : $f(4) = \dfrac{4}{2} + 6 = 2 + 6 = 8$ .

Question 8easy

The function $f(x)$ is defined by $f(x) = -3x + 20$ . For what value of $x$ does $f(x) = 5$ ?

Set $-3x + 20 = 5$ . Then $-3x = -15$ , so $x = 5$ .

Evaluating functions at a value practice