Corbettmaths: Evaluating Functions

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Questions and Answers

If $f(x) = 3x + 5$, what is $f(0)$?

5

If $g(x) = \frac{2x + 9}{4}$, what is $g(0)$?

9/4

If $h(x) = x^2 - 5$, what is $h(7)$?

44

If $f(x) = 3x - 8$, solve for $x$ when $f(x) = 7$.

<p>5</p> Signup and view all the answers

If $g(x) = 19 - 4x$, solve for x when $g(x) = 31$.

<p>-3</p> Signup and view all the answers

If $h(x) = \frac{5x - 1}{2}$, solve for $x$ when $h(x) = 32$.

<p>13</p> Signup and view all the answers

If $f(x) = x^2 - 2x + 3$, solve for $x$ when $f(x) = 27$.

<p>-4, 6</p> Signup and view all the answers

If $f(x) = x + 5$ and $g(x) = 3x - 1$, what is the value of $g(1)$?

<p>2</p> Signup and view all the answers

If $g(x) = 3x - 8$, what is $g(-2)$?

<p>-14</p> Signup and view all the answers

If $f(x) = \frac{32}{x^2}$, what is $f(4)$?

<p>2</p> Signup and view all the answers

If $g(x) = 2x^3$, what is $g(1)$?

<p>2</p> Signup and view all the answers

If $f(x) = 2x + 1$ and $g(x) = x - 5$, what is $g(x)$?

<p>x - 5</p> Signup and view all the answers

If $h(x) = x^2$, what is $h(x)$?

<p>x^2</p> Signup and view all the answers

If $f(x) = 2x$, what is $f^{-1}(x)$?

<p>x/2</p> Signup and view all the answers

If $f(x) = x - 6$, what is $f^{-1}(x)$?

<p>x+6</p> Signup and view all the answers

If $h(x) = \frac{x}{4}$, what is $h^{-1}(x)$?

<p>4x</p> Signup and view all the answers

Flashcards

What is a function?

A mathematical rule that assigns each input value to a single output value.

What is evaluating a function?

Substituting a given value into a function and calculating the result.

What is substitution in functions?

Replacing the variable 'x' in the function's expression with the specified value.

What does 'Solve f(x) = a' mean?

Finding the 'x' value(s) that make the function equal to a specific value.

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What is composite function?

A function created by applying one function to the result of another.

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What is an inverse function?

Denoted as f⁻¹(x), reverses the action of the original function f(x).

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What is function composition?

A function composition where the inner function's output becomes the outer function's input.

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What does solve f(a) = g(a) mean?

Finding the input value 'a' for which the outputs of two functions, f(a) and g(a), are equal.

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Study Notes

  • Functions are covered in Corbettmaths videos 369 and 370.

Function Evaluation

  • To evaluate a function f(x) at a specific value, substitute that value for x in the function's expression.
  • For a function g(x), g(a) means replacing x with a in the expression defining g.
  • When given f(x) = some expression, solving f(x) = a constant involves finding the x value that makes the function equal to that constant.
  • Composite functions, like fg(x), involve substituting the function g(x) into the function f(x).
  • The inverse of h(x) is denoted as h⁻¹(x).
  • To find a value "a" such that f(a) = g(a), set the expressions for f(x) and g(x) equal to each other and solve for x.
  • To express a function in the form ax² + bx + c, expand and simplify the expression for the function.
  • For functions f(x) and g(x), solving fg(x) = gf(x) involves finding the x values for which the composite functions are equal.
  • To show that f(x + 1) - f(x) = some expression, substitute (x + 1) into f(x), subtract f(x), and simplify to match the given expression.

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