Math Problem Statement

What is the average value of cos(x) on the interval [-2, 7]?

Solution

To solve for the average value of cos(x)\cos(x) on the interval [2,7][-2, 7], we use the formula for the average value of a continuous function f(x)f(x) over an interval [a,b][a, b]:

Average value of f(x)=1baabf(x)dx\text{Average value of } f(x) = \frac{1}{b - a} \int_a^b f(x) \, dx

In this case, f(x)=cos(x)f(x) = \cos(x), a=2a = -2, and b=7b = 7. Plugging these into the formula, we have:

Average value of cos(x)=17(2)27cos(x)dx\text{Average value of } \cos(x) = \frac{1}{7 - (-2)} \int_{-2}^7 \cos(x) \, dx

Simplifying:

Average value of cos(x)=1927cos(x)dx\text{Average value of } \cos(x) = \frac{1}{9} \int_{-2}^7 \cos(x) \, dx

Now, we calculate the integral of cos(x)\cos(x):

cos(x)dx=sin(x)\int \cos(x) \, dx = \sin(x)

So, we evaluate sin(x)\sin(x) at the limits:

[sin(x)]27=sin(7)sin(2)\left[ \sin(x) \right]_{-2}^7 = \sin(7) - \sin(-2)

Since sin(x)=sin(x)\sin(-x) = -\sin(x), this becomes:

sin(7)+sin(2)\sin(7) + \sin(2)

Now the average value is:

19(sin(7)+sin(2))\frac{1}{9} \left( \sin(7) + \sin(2) \right)

Using approximate values for sin(7)0.657\sin(7) \approx 0.657 and sin(2)0.909\sin(2) \approx 0.909, we get:

Average value19×(0.657+0.909)=19×1.5660.174\text{Average value} \approx \frac{1}{9} \times (0.657 + 0.909) = \frac{1}{9} \times 1.566 \approx 0.174

So, the average value of cos(x)\cos(x) on the interval [2,7][-2, 7] is approximately 0.174.

Would you like further details or have any questions?

Here are 5 related questions:

  1. What is the geometric meaning of the average value of a function?
  2. How does the average value of sin(x)\sin(x) differ from that of cos(x)\cos(x)?
  3. Can the average value formula be used for non-trigonometric functions? How?
  4. How does changing the interval affect the average value of cos(x)\cos(x)?
  5. What is the average value of cos(x)\cos(x) on [0,2π][0, 2\pi]?

Tip: Understanding how to evaluate definite integrals is crucial for finding the average value of a function.

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Math Problem Analysis

Mathematical Concepts

Calculus
Definite Integrals
Average Value of a Function

Formulas

Average value of f(x) = (1 / (b - a)) ∫ from a to b f(x) dx
∫ cos(x) dx = sin(x)

Theorems

Fundamental Theorem of Calculus

Suitable Grade Level

Grades 11-12, College-level Calculus