20. The interior angles of an octagon are [tex]2x^{\circ}, \frac{1}{2} x^{\circ}, (x+40)^{\circ}, 110^{\circ}, 135^{\circ}, 160^{\circ}, (2x+10)^{\circ}[/tex] and [tex]185^{\circ}[/tex]. Find the value of [tex]x[/tex].

(3 marks)



Answer :

To find the value of [tex]\(x\)[/tex] in the given problem, we need to use the fact that the sum of the interior angles of an octagon is always 1080 degrees. The interior angles provided are [tex]\(2x^\circ\)[/tex], [tex]\(\frac{1}{2}x(x + 40)^\circ\)[/tex], [tex]\(110^\circ\)[/tex], [tex]\(135^\circ\)[/tex], [tex]\(160^\circ\)[/tex], [tex]\((2x + 10)^\circ\)[/tex], and [tex]\(185^\circ\)[/tex].

Here is the step-by-step solution:

1. Write down the sum of the angles:

We know the sum of these angles must equal 1080 degrees.

2. Form the equation:

[tex]\[ 2x + \frac{1}{2}x(x + 40) + 110 + 135 + 160 + (2x + 10) + 185 = 1080 \][/tex]

3. Combine like terms:

Combine all the constants together:

[tex]\[ 110 + 135 + 160 + 10 + 185 = 600 \][/tex]

So, the equation now becomes:

[tex]\[ 2x + \frac{1}{2}x(x + 40) + 2x + 600 = 1080 \][/tex]

4. Simplify further:

Combine the [tex]\(x\)[/tex] terms:

[tex]\[ 4x + \frac{1}{2}x(x + 40) + 600 = 1080 \][/tex]

5. Clear the parenthesis:

Distribute [tex]\(\frac{1}{2}x\)[/tex] inside the parentheses:

[tex]\[ \frac{1}{2}x^2 + 20x \][/tex]

Therefore, the equation becomes:

[tex]\[ 4x + \frac{1}{2}x^2 + 20x + 600 = 1080 \][/tex]

6. Combine like terms:

Combine the [tex]\(x\)[/tex] terms again:

[tex]\[ \frac{1}{2}x^2 + 24x + 600 = 1080 \][/tex]

7. Move all terms to one side to set the equation to 0:

[tex]\[ \frac{1}{2}x^2 + 24x + 600 - 1080 = 0 \][/tex]

This simplifies to:

[tex]\[ \frac{1}{2}x^2 + 24x - 480 = 0 \][/tex]

8. Multiply through by 2 to clear the fraction:

[tex]\[ x^2 + 48x - 960 = 0 \][/tex]

9. Solve the quadratic equation:

Using the quadratic formula [tex]\(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\)[/tex], where [tex]\(a = 1\)[/tex], [tex]\(b = 48\)[/tex], and [tex]\(c = -960\)[/tex]:

[tex]\[ x = \frac{-(48) \pm \sqrt{48^2 - 4 \cdot 1 \cdot (-960)}}{2 \cdot 1} \][/tex]

Simplify under the square root:

[tex]\[ x = \frac{-48 \pm \sqrt{2304 + 3840}}{2} \][/tex]

[tex]\[ x = \frac{-48 \pm \sqrt{6144}}{2} \][/tex]

[tex]\[ x = \frac{-48 \pm 78.431}{2} \][/tex]

10. Solve for the two potential values of [tex]\(x\)[/tex]:

[tex]\[ x_1 = \frac{-48 + 78.431}{2} \][/tex]
[tex]\[ x_1 \approx 15.1918358845308 \][/tex]

[tex]\[ x_2 = \frac{-48 - 78.431}{2} \][/tex]
[tex]\[ x_2 \approx -63.1918358845308 \][/tex]

However, since [tex]\(x\)[/tex] represents an angle measure, it cannot be negative. Thus, the valid solution for [tex]\(x\)[/tex] is:

[tex]\[ x \approx 15.1918358845308 \][/tex]