Math Problem Statement

The function f: x → e^{x^2} is defined for all x ∈ R. (i) Find f'(x) and f''(x). (ii) Find the turning point of the curve y = e^{x^2}. (iii) Determine whether this turning point is a local maximum or a local minimum.

Solution

Let's solve the problem from the image step-by-step. The function given is f(x)=ex2f(x) = e^{x^2}, and we are asked to do the following:

(i) Find f(x)f'(x) and f(x)f''(x).

  1. First Derivative f(x)f'(x):

    The function is f(x)=ex2f(x) = e^{x^2}. To differentiate this, we use the chain rule. The derivative of eue^u with respect to uu is eue^u, and the derivative of x2x^2 with respect to xx is 2x2x.

    Therefore, f(x)=ddx(ex2)=ex22x=2xex2.f'(x) = \frac{d}{dx} \left( e^{x^2} \right) = e^{x^2} \cdot 2x = 2x e^{x^2}.

  2. Second Derivative f(x)f''(x):

    Now, to find the second derivative, we differentiate f(x)=2xex2f'(x) = 2x e^{x^2} using the product rule. The product rule states (uv)=uv+uv(uv)' = u'v + uv'.

    Let u=2xu = 2x and v=ex2v = e^{x^2}.

    • u=2u' = 2
    • v=2xex2v' = 2x e^{x^2} (from the first derivative we calculated earlier)

    Using the product rule: f(x)=ddx(2xex2)=2ex2+2x2xex2=2ex2+4x2ex2.f''(x) = \frac{d}{dx}(2x e^{x^2}) = 2 \cdot e^{x^2} + 2x \cdot 2x e^{x^2} = 2e^{x^2} + 4x^2 e^{x^2}. Simplifying this: f(x)=ex2(2+4x2).f''(x) = e^{x^2} (2 + 4x^2).

(ii) Find the turning point of the curve y=ex2y = e^{x^2}.

A turning point occurs when f(x)=0f'(x) = 0. From part (i), we have f(x)=2xex2f'(x) = 2x e^{x^2}.

For f(x)=0f'(x) = 0, either 2x=02x = 0 or ex2=0e^{x^2} = 0. Since ex2e^{x^2} is never zero, we have:

2x=0x=0.2x = 0 \quad \Rightarrow \quad x = 0.

So, the turning point occurs at x=0x = 0. To find the corresponding yy-value, we substitute x=0x = 0 into f(x)=ex2f(x) = e^{x^2}:

y=e02=e0=1.y = e^{0^2} = e^0 = 1.

Thus, the turning point is (0,1)(0, 1).

(iii) Determine whether this turning point is a local maximum or a local minimum.

To classify the turning point, we examine the second derivative f(x)=ex2(2+4x2)f''(x) = e^{x^2}(2 + 4x^2) at x=0x = 0:

f(0)=e02(2+4(0)2)=e02=2.f''(0) = e^{0^2}(2 + 4(0)^2) = e^0 \cdot 2 = 2.

Since f(0)>0f''(0) > 0, the function is concave up at x=0x = 0, meaning the turning point is a local minimum.

Summary:

  1. f(x)=2xex2f'(x) = 2x e^{x^2}
  2. f(x)=ex2(2+4x2)f''(x) = e^{x^2}(2 + 4x^2)
  3. The turning point is (0,1)(0, 1)
  4. The turning point is a local minimum.

Would you like any further details on these steps, or do you have any specific questions?

Here are some related questions you could explore:

  1. How do you find the third derivative of f(x)=ex2f(x) = e^{x^2}?
  2. What happens to f(x)f(x) as xx \to \infty?
  3. How do you classify points of inflection for f(x)=ex2f(x) = e^{x^2}?
  4. Can you find the Taylor series expansion of f(x)=ex2f(x) = e^{x^2}?
  5. How does the behavior of the function change for negative values of xx?

Tip: The second derivative test is a powerful tool to quickly determine the concavity of a function and classify its turning points.

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Math Problem Analysis

Mathematical Concepts

Differentiation
Chain Rule
Product Rule
Turning Points
Second Derivative Test

Formulas

f'(x) = 2x e^{x^2}
f''(x) = e^{x^2}(2 + 4x^2)

Theorems

Second Derivative Test

Suitable Grade Level

Grades 11-12 (Advanced High School Calculus)