# Give an example of a function, f(x), that has an inflection point at (1, 4).

justaguide | College Teacher | (Level 2) Distinguished Educator

Posted on

An inflection point of a function f(x) is the point where the curvature changes sign. When that happens f''(x) = 0.

Here an example of a function is required that has a point of inflection at (1, 4). Let the function be f(x).

f''(1) = 0

Let f''(x) = 6x - 6

f'(x) = 3x^2 - 6x + C

f(x) = x^3 - 3x^2 + C1*x + C2

f(1) = 4

=> 1^3 - 3*1 + C1*1 + C2 = 4

Let C2 = 0

=> C1 = 6

An example of a function that has an inflection point at (1,4) is f(x) = x^3 - 3x^2 + 6x

colege | Student, College Freshman | (Level 1) Honors

Posted on

Hm if possible, could i have another expert answer? Its on my math review  sheet and i wake to make sure :%

giorgiana1976 | College Teacher | (Level 3) Valedictorian

Posted on

The function has an inflection point when the 2nd derivative is cancelling out.

We'll have to choose a function of 3rd order, to be differentiated twice.

f(x) = ax^3 + bx^2 + cx + d

We'll differentiate with respect to x:

f'(x) = 3ax^2 + 2bx + c

We'll differentiate with respect to x again:

f"(x) = 6ax + 2b

We'll put f"(x) = 0 for x = 1

6a + 2b = 0

3a + b = 0

b = -3a

We'll calculate f'(1) = 3a + 2b + c

f'(1) = b + c

f(1) = a + b + c + d

But f(1) = 4

a + b + c + d = 4

To determine the function f(x), it would be necessary to provide another constraint concerning the 1st derivative, otherwise, the coefficients cannot be determined under the circumstances.

But, you have to remember that the function is a polynomial  of 3rd order, at least: f(x) = ax^3 + bx^2 + cx + d.