Question Progress

Homework Progress: [tex]$7 / 50$[/tex]

a) Show that the equation [tex]x^3 + 6x - 5 = 0[/tex] has a solution between [tex]x = 0[/tex] and [tex]x = 1[/tex].

Show your working.

b) Show that the equation [tex]x^3 + 6x - 5 = 0[/tex] can be rearranged to give [tex]x = \frac{5}{x^2 + 6}[/tex] by filling in the boxes.

[tex]x^3 + 6x - 5 = 0[/tex]

[tex]\square \; x^3 + 6x =[/tex]

[tex]\square[/tex]

[tex]\square \; (x^2 + 6) =[/tex]

[tex]x = \frac{5}{x^2 + 6}[/tex]



Answer :

Certainly! Let's address each part of the question in a detailed step-by-step manner.

### Part (a)

We are asked to show that the equation [tex]\( x^3 + 6x - 5 = 0 \)[/tex] has a solution between [tex]\( x = 0 \)[/tex] and [tex]\( x = 1 \)[/tex].

1. Evaluate the function at [tex]\( x = 0 \)[/tex]:
[tex]\[ f(0) = 0^3 + 6 \cdot 0 - 5 = -5 \][/tex]

2. Evaluate the function at [tex]\( x = 1 \)[/tex]:
[tex]\[ f(1) = 1^3 + 6 \cdot 1 - 5 = 1 + 6 - 5 = 2 \][/tex]

3. Analyze the signs of [tex]\( f(0) \)[/tex] and [tex]\( f(1) \)[/tex]:
[tex]\[ f(0) = -5 \quad \text{(negative)}, \quad f(1) = 2 \quad \text{(positive)} \][/tex]

Given that [tex]\( f(0) \)[/tex] is negative and [tex]\( f(1) \)[/tex] is positive, and since [tex]\( f(x) \)[/tex] is a continuous function (as it is a polynomial), by the Intermediate Value Theorem, there must be at least one root of the equation [tex]\( x^3 + 6x - 5 = 0 \)[/tex] in the interval [tex]\( (0, 1) \)[/tex].

Thus, the equation [tex]\( x^3 + 6x - 5 = 0 \)[/tex] has a solution between [tex]\( x = 0 \)[/tex] and [tex]\( x = 1 \)[/tex].

### Part (b)

We need to show how the equation [tex]\( x^3 + 6x - 5 = 0 \)[/tex] can be rearranged to give [tex]\( x = \frac{5}{x^2 + 6} \)[/tex] by filling in the boxes in the provided template.

1. Starting with the given equation:
[tex]\[ x^3 + 6x - 5 = 0 \][/tex]

2. Move the constant term to the right-hand side:
[tex]\[ x^3 + 6x = 5 \][/tex]

3. Express [tex]\( x \)[/tex] in terms of the remaining expression:
[tex]\[ x = \frac{5}{x^2 + 6} \][/tex]

We can now fill in the boxes:

- For the template:
[tex]\[ x^3 + 6x = \square \][/tex]

The filled answer is:
[tex]\[ x^3 + 6x = 5 \][/tex]

- For the template:
[tex]\[ \square \left(x^2 + 6\right) = x \][/tex]

Rearranging [tex]\( x = \frac{5}{x^2 + 6} \)[/tex] to [tex]\(5 = x \cdot \left( x^2 + 6 \right)\)[/tex], the filled answer is:
[tex]\[ 5 = x \left(x^2 + 6\right) \][/tex]

Thus, we have shown that the equation [tex]\( x^3 + 6x - 5 = 0 \)[/tex] can indeed be rearranged into [tex]\( x = \frac{5}{x^2 + 6} \)[/tex].