How to Find Turning Points of a Function – A Step-by-Step Guide

How to Find Turning Points of a Function A Step-by-Step Guide

To find turning points of a function, you should first understand what a turning point is: it’s a point on the graph of a function where the direction of the curve changes.

In mathematical terms, at a turning point, the derivative of the function will be zero. This is because the slope of the tangent to the graph at a turning point is zero, indicating a transition from increasing to decreasing, or vice versa. 

By setting the derivative of the function equal to zero, you can solve for the x-values that may correspond to these crucial points.

After finding the x-values, you should evaluate the function at these points to find the corresponding y-values, completing the coordinates of the turning points.

Graphically, these turning points can be either peaks or valleys on the curve, known as local maxima or minima. To distinguish between them and identify the nature of each turning point, you can use the second derivative test or analyze the behavior of the function on intervals surrounding these points.

Stay tuned, as I’ll be walking you through these steps, ensuring you can confidently locate and interpret the turning points of any function, which is a vital skill in understanding the nature of mathematical graphs and in solving many practical problems.

Identifying Turning Points of a Function

When analyzing the behavior of a function, particularly polynomial functions like quadratic or cubic, I often look for their turning points.

Turning points are where a function changes from increasing to decreasing, or vice versa—essentially the peaks and troughs of the graph. These points are not just visually recognizable but also can be calculated using the derivative of the function.

To find the turning points, I follow these steps:

  1. Find the Derivative: The derivative ( f'(x) ) of a function ( f(x) ) gives me the rate of change. For turning points, the rate changes sign, so I need to find where ( f'(x) = 0 ).

  2. Solve for Critical Points: Setting the derivative equal to zero ( f'(x) = 0 ) and solving this equation gives me the x-values, which are possible turning points.

  3. Determine Maximum or Minimum: To find out if these critical points are a maximum or minimum value, I’ll use the second derivative test. If ( f”(x) > 0 ), the point is a minimum; if ( f”(x) < 0 ), it’s a maximum.

1. DerivativeCompute ( f'(x) )
2. Critical PointsSolve ( f'(x) = 0 )
3. Max or MinUse ( f”(x) ) to determine the nature of turning points

For polynomial graphs, the number of turning points is at most the degree of the polynomial minus one. So, a quadratic function can have up to 1 turning point, while a cubic function can have up to 2.

Understanding the relationship between the function, its graph, and its derivative helps to reveal where the function is increasing or decreasing and locate those important turning points effectively.

Analyzing the Function’s Behavior

When I begin to analyze the behavior of a polynomial function, my first step is considering its degree. The degree gives me vital clues about the function’s shape and end behavior.

It’s interesting to note that a polynomial of degree ( n ) can have up to ( n-1 ) turning points; that’s the maximum number of turning points it can have.

Continuous functions like polynomials don’t make sudden jumps, so their graphs are smooth curves. As I look at the graph, I pay attention to where it intersects the axes, since the x-intercepts signify the function’s zeros, and the y-intercept is the point where the function crosses the y-axis, which occurs when ( x = 0 ).

DegreePossible Number of Turning Points

Next, I consider the end behavior by examining the limits as ( x ) approaches positive and negative infinity. If the degree is even, the ends of the graph will point in the same direction; if odd, they’ll point in opposite directions.

To find the exact turning points, I look for where the function’s derivative equals zero. The derivative indicates the function’s rate of change, and where it’s zero, the graph may have a peak or a valley – a local maximum or minimum, i.e., the local behavior of the function.

Lastly, a sketch of the graph helps visualize these elements concretely. Through graphing, I can interpret the signs and behavior of the function across different intervals and confirm the position of turning points.


In my exploration of turning points, I have discussed methods for determining where a function’s graph curves and changes direction. Such points are crucial in understanding the behavior of polynomial equations and other mathematical functions.

To recap, turning points are found by solving for when the derivative, denoted as $f'(x)$, equals zero. This entails setting $f'(x) = 0$ and finding the $x$ values.

After pinpointing the $x$ values, I determine the $y$ coordinates by substituting these $x$ values back into the original function, $f(x)$. The resulting coordinates represent the location of turning points on the graph.

It’s important to remember that a turning point is where the graph changes from increasing to decreasing or vice versa, which can be a local maximum, local minimum, or a point of inflection.

Additionally, the degree of the polynomial plays a role in the maximum number of turning points it can have, which is always less than its degree.

Understanding the concept of multiplicity is equally important because it affects how the graph behaves at the zeros. If a zero has an even multiplicity, the graph touches the x-axis and turns around. With an odd multiplicity, it crosses the axis.

By applying calculus and algebraic techniques, anyone can sketch the behavior of functions and predict their turning points.

This is not just an academic exercise but a powerful tool in fields ranging from physics to economics, where the optimization of outcomes often hinges on these crucial points on a graph.