Question

What is the value of $ f\left( 5 \right) $ for the function $ f\left( x \right) = 3x - 4 $ ?

Answer 1

Hint: We have to find $ f\left( 5 \right) $ for the function $ f\left( x \right) = 3x - 4 $ , that means we have to substitute 5 in place of x in the given function and then solve the equation. Solving the equation we will get our answer.

Complete step by step solution:
In this question, we are given a function $ f\left( x \right) = 3x - 4 $ and we have to find what its value is for $ f\left( 5 \right) $ .
Let us understand the given function $ f\left( x \right) = 3x - 4 $ .
Here, f is a function in terms of $ x $ . As you can see, variable $ x $ is used in the equation. Hence, it is denoted by $ f\left( x \right) $ .
If the equation was in term of $ y $ , for example let us take an equation
 $ 4y - 9 $ , then it will be denoted by $ f\left( y \right) $ .
So, the term in brackets is nothing but the variable used in the equation.
Now, we have to find the value of $ f\left( 5 \right) $ for the equation $ f\left( x \right) = 3x - 4 $ .
That means we have to put 5 in place of the variable used in the equation.
That means we have to substitute $ x $ as 5 in the given equation.
Therefore,
 $ \Rightarrow f\left( 5 \right) = 3\left( 5 \right) - 4 $
$
   = 15 - 4 \\
   = 11 \;
  $
Hence, the value of $ f\left( 5 \right) $ for $ f\left( x \right) = 3x - 4 $ is 11.
So, the correct answer is “ 11”.

Note: If we are given two variables in an equation and then we are asked to find the value of equation at particular point, for example: $ f\left( x \right) = 3x - 4y $ and find $ f\left( 5 \right) $ . Here, there are two variables in the equation, but our function is $ f\left( x \right) $ . So, we have to substitute 5 in place of x only.
 $ \Rightarrow f\left( x \right) = 3x - 4y = 3\left( 5 \right) - 4y = 15 - 4y $