Problem 36 - Calculus: Graphical, Numerical, Algebraic

Question

True or False The graph of \(f(x)=|x|\) has a tangent line at \(x=0,\) Justify your answer.

Step-by-Step Solution

Answer

False. The function \(f(x)=|x|\) does not have a tangent line at \(x=0\) because the derivative doesn't exist at \(x=0\); therefore, the horizontal line isn't well-defined.

Step 1: Understand the graph

The graph of the function \(f(x)=|x|\) splits into two parts for negative and positive values, forming a 'v' shape. At \(x=0\), it's the vertex part of the graph.

Step 2: Derive the function

We need the derivative to check the slope of the tangent line. But the function \(f(x)=|x|\) is not differentiable at \(x=0\), as a result of the |.| function which causes a sharp turn at \(x = 0\) .

Step 3: Analyze the derivative

Since there exists a sharp point at \(x=0\), we say \(f'(0)\) does not exist. So we can't uniquely define a line whose slope equals \(f'(0)\).

Key Concepts

Derivative

In calculus, the derivative of a function plays a crucial role in determining the slope of a tangent line to the graph of that function at any given point. To derive a function analytically means calculating its rate of change for any value of its input, often denoted as \( f'(x) \).

For the function \( f(x) = |x| \), derivatives are mostly straightforward to find, except at points of discontinuity or sharp turns, like at \( x=0 \). For negative \( x \), \( f(x) = -x \), thus \( f'(x) = -1 \), and for positive \( x \), \( f(x) = x \), hence \( f'(x) = 1 \). However, at \( x=0 \), the behavior of the derivatives from left (\( -1 \)) and right (\( 1 \)) do not match, indicating a lack of a single, well-defined slope.

Derivatives help us understand the behavior of functions and whether we can define tangent lines at specific points. This concept is foundational to studying motion, optimization, and analyzing variable rate changes in broader mathematics and applied science.

Differentiability

Differentiability is concerned with whether a function has a derivative that exists at a particular point. A function is differentiable if it can be smoothly drawn without any sharp turns or cusps.

In the function \( f(x) = |x| \), differentiability is absent at \( x=0 \) due to the abrupt change in the graph, forming a 'v' shape. For a function to be differentiable at \( x \), the left-hand limit and right-hand limit of \( \frac{f(x+h) - f(x)}{h} \) as \( h \to 0 \) must equal and give consistent results.

A lack of differentiability means no single tangent line can gracefully touch the graph at that point without piercing through. In this case, the sharp turn at the vertex contributes to a non-existent slope at \( x = 0 \), rendering any tangent effort fruitless.

Graph Analysis

Graph analysis is a fundamental skill in understanding the behavior and properties of functions by visualizing them. It involves inspecting the shape and features of the function's graph to deduce important mathematical properties.

The graph of \( f(x) = |x| \) reveals much about the function through its distinctive 'v' shape. By plotting the graph, we identify a vertex at \( x=0 \) where two linear pieces meet.

Having a sharp point like this signifies a transition in behavior, which often impacts differentiability and computation of a tangent. Detailed graph analysis helps recognize symmetry, intervals of increase or decrease, and abrupt transitions like the one seen here.

Tangent Line

A tangent line to a function at a specific point is a straight line that just touches the curve at that point, mimicking the function's slope there. The characteristic of a tangent line is that it has the same derivative as the function at the point of tangency.

In the exercise, finding a tangent line at \( x=0 \) for \( f(x) = |x| \) is impossible due to the derivative not existing at this point. If a derivative can't be identified due to significant slope variation like from \(-1\) to \(1\) at a cusp, then a unique tangent line cannot be drawn.

This underscores the important relationship between differentiability and tangents: where differentiability fails, so does the construction of a reliable tangent line. Understanding this is vital for accurately predicting the behavior of functions and managing applications that require smooth transitions.