   Chapter 2.5, Problem 57E ### Single Variable Calculus: Early Tr...

8th Edition
James Stewart
ISBN: 9781305270343

#### Solutions

Chapter
Section ### Single Variable Calculus: Early Tr...

8th Edition
James Stewart
ISBN: 9781305270343
Textbook Problem

# (a) Prove that the equation has at least one real root. (b) Use your calculator to find an interval of length 0.01 that contains a root.cos x = x3

(a)

To determine

To prove: The equation cosx=x3 has at least one real root.

Explanation

Theorem used: The Intermediate value Theorem

Suppose that if f is continuous on the closed interval [a, b] and let N be any number between f(a) and f(b), where f(a)f(b). Then there exists a number c in (a, b) such that f(c)=N.

Proof:

Rewrite the equation as follows, x3cosx=0.

Consider the function f(x)=x3cosx.

The function f(x) is a combination of polynomial and trigonometric function. So it is continuous everywhere on its domain (,).

Without loss of generality, take the subinterval [0,1].

In order to show that there is a root of the equation x3cosx=0 in the interval (0,1), it is enough to show that there is a number c between 0 and 1 for which f(c)=0.

Take a=0, b=1 and N=0

(b)

To determine

To find: An interval of length 0.01 that contains a root by using the calculator.

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