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Sep 21, 2014 · For a quadratic function ax2 +bx + c, we can determine the concavity by finding the second derivative. f (x) = ax2 + bx +c. f '(x) = 2ax +b. f ''(x) = 2a. In any function, if the second derivative is positive, the function is concave up. If the second derivative is negative, the function is concave down.
Review your knowledge of concavity of functions and how we use differential calculus to analyze it.
- Definition of Concavity
- Theorem
- Definition of Point of Inflection
Let f′f′ be the first derivative of function ff that is differentiable on a given interval II, the graph of ff is (i) concave up on the interval II, if f′f′ is increasing on II, or (ii) concave down on the interval II, if f′f′ is decreasing on II. The sign of the second derivative informs us when f′f′is increasing or decreasing.
Let f″f′′ be the second derivative of function ff on a given interval II, the graph of ff is (i) concave up on II if f″(x)>0f′′(x)>0 on the interval II. (ii) concave down on II if f″(x)<0f′′(x)<0 on the interval II.
A point PP on the graph of y=f(x)y=f(x) is a point of inflection if ff is continuous at PP and the concavity of the graph changes at PP. In view of the above theorem, there is a point of inflection whenever the second derivative changes sign.
How do you determine the concavity of a quadratic function? How do you find the concavity of a rational function? What is the concavity of a linear function? What x values is the function concave down if #f (x) = 15x^ (2/3) + 5x#? How do you know concavity inflection points, and local min/max for #f (x) = 2x^3 + 3x^2 - 432x#?
If given a graph of f (x) or f' (x), determining concavity is relatively simple. Otherwise, the most reliable way to determine concavity is to use the second derivative of the function; the steps for doing so as well as an example are located at the bottom of the page.
As in one variable calculus, the purely quadratic terms tell us about how the graph is bending. In particular, if the quadratic part is positive away from (a;b), the function is convex (also known as concave up) and if the quadratic part is negative, the function is concave down. We will use this to create a second-derivative test
Jan 13, 2014 · The graph of a quadratic function is called a parabola. Notice that the function in Figure 3.1 is con-cave down and has a maximum corresponding to the time at which the ball stops rising and begins to fall back to the earth. The maximum point on the parabola is called the vertex.