x-4 ; x+2 ; 3x+1 ; ... are the first three terms of a geometric sequence Determine the sequence if x is positive.​

Respuesta :

Answer:

x = 8

Step-by-step explanation:

This sequence is a geometric sequence.

As it is a geometric sequence, It means that each term multiply by a value that we call that value "a".

So (x-4) × a = (x + 2)

Therefore [tex]\frac{x+2}{x-4} = a[/tex]

And (x+2) × a = (3x+1)

Therefore [tex]\frac{3x+1}{x+2} =a[/tex].

By this we can make a conclusion that [tex]\frac{3x+1}{x+2} =\frac{x+2}{x-4}[/tex].

  1. [tex]\frac{3x+1}{x+2}= \frac{x+2}{x-4}[/tex]
  2. [tex](3x + 1) * (x-4) = (x+2) * (x+2)[/tex]
  3. [tex]3x^{2} -11x-4=x^{2} +4x+4[/tex]
  4. [tex]2x^{2} -15x-8 = 0[/tex]
  5. [tex](2x+1) * (x-8) = 0[/tex]

In the last part one of the parentheses should be 0.

First we put (2x+1) equal to 0.

  1. [tex]2x+1 = 0[/tex]
  2. [tex]2x = -1[/tex]
  3. [tex]x = -\frac{1}{2}[/tex]

It gives us a negative answer, so this is not our answer.

Now we put (x-8) equal to 0.

  1. [tex]x-8=0[/tex]
  2. [tex]x = 8[/tex]

This is a positive answer and it is correct.

and the terms are 4, 10, 25 , ...

Please choose my answer as the brainliest answer.

Answer:

  • 4, 10, 25, 62.5, ...

Step-by-step explanation:

Given GP:

  • x - 4, x + 2, 3x + 1, ...

Common ratio is:

  • (x + 2)/(x - 4) = (3x + 1)/(x + 2)

Cross-multiply and solve for positive x:

  • (x + 2)² = (x - 4)(3x + 1)
  • x² + 4x + 4 = 3x² - 11x - 4
  • 2x² - 15x - 8 = 0
  • x = (15 + √(15² + 4*2*8))/4
  • x = (15 + 17)/4
  • x = 8

The first term is:

  • 8 - 4 = 4

The common ratio is:

  • (8 + 2)/4 = 2.5

The nth term is:

  • aₙ = 4*(2.5)ⁿ ⁻ ¹

The sequence is:

  • 4, 10, 25, 62.5, ...