요금제

합성함수 계산기

이 계산기는 두 다항함수에 대해 f(g(x))와 g(f(x))를 구해 전개하고, 선택한 x 값에서 둘 다 계산합니다. 예를 들어 f(x) = 2x + 3, g(x) = x²이면 f(g(x)) = 2x² + 3, g(f(x)) = 4x² + 12x + 9입니다.

수 또는 분수

결과

값을 입력하고 계산을 누르면 결과가 표시됩니다.

공식

(f∘g)(x)=f(g(x))(f \circ g)(x) = f(g(x))

Apply g first, then f: replace every x in f with g(x).

(g∘f)(x)=g(f(x))(g \circ f)(x) = g(f(x))

The other order. In general f(g(x)) and g(f(x)) are different.

이 계산기 사용법

  1. Type f(x) and g(x) as polynomials, e.g. 2x + 3 and x^2.
  2. Choose a value of x to evaluate the composite functions at.
  3. Press Calculate to see f(g(x)) and g(f(x)) expanded, their values, and the substitution steps. To graph the function, open it in the graphing calculator.

풀이 예제

f(g(x)) and g(f(x)) for a linear and a quadratic function

f(g(x)): replace x in 2x + 3 with x², giving 2x² + 3.

g(f(x)): square 2x + 3, giving 4x² + 12x + 9.

At x = 2: g(2) = 4, so f(g(2)) = 11; f(2) = 7, so g(f(2)) = 49.

A shift inside a quadratic

f(g(x)) = (x + 1)² − 1 = x² + 2x.

g(f(x)) = (x² − 1) + 1 = x².

At x = 3: f(g(3)) = f(4) = 15 and g(f(3)) = g(8) = 9.

A cubic composed with a linear function

f(g(x)) = (x − 2)³ = x³ − 6x² + 12x − 8.

g(f(x)) = x³ − 2.

At x = 1 both are −1: (1 − 2)³ = −1 and 1³ − 2 = −1.

자주 하는 실수

  • Multiplying instead of composing: f(g(x)) is not f(x)·g(x).
  • Working in the wrong order: f(g(x)) applies g first.
  • Substituting without brackets: with g(x) = x + 1, f(x) = x² gives (x + 1)², not x² + 1.
  • Assuming f(g(x)) = g(f(x)) — it usually isn’t.

자주 묻는 질문

How do you find f of g of x?

Write f(x), then replace every x with the whole expression g(x) in brackets, and simplify. For f(x) = 2x + 3 and g(x) = x², f(g(x)) = 2x² + 3.

What is the domain of a composite function?

The x-values in the domain of g whose output g(x) is in the domain of f. For the polynomials this calculator takes, both domains are all real numbers, so f(g(x)) is defined everywhere.

Can I graph the function?

Yes — copy f(g(x)) into the Sumzo graphing calculator to plot it, see where it crosses the x-axis and read a table of values.

Which functions can I enter?

Polynomials up to degree 6, such as 3x^2 - x + 4 or (x + 1)^3. Fractions like 1/2 x work as coefficients.

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