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If [tex]$x, 4x + 3,$[/tex] and [tex]$7x + 6$[/tex] are consecutive terms of a geometric sequence, find the value(s) of [tex][tex]$x$[/tex][/tex].

Sagot :

Alright, let's find the value(s) of [tex]\( x \)[/tex] given that [tex]\( x \)[/tex], [tex]\( 4x + 3 \)[/tex], and [tex]\( 7x + 6 \)[/tex] are consecutive terms of a geometric sequence.

In a geometric sequence, the ratio between consecutive terms is constant. Let the common ratio be [tex]\( r \)[/tex].

1. The ratio of the second term to the first term should equal the ratio of the third term to the second term:
[tex]\[ r = \frac{4x + 3}{x} = \frac{7x + 6}{4x + 3}. \][/tex]

2. Set up the equation:
[tex]\[ \frac{4x + 3}{x} = \frac{7x + 6}{4x + 3}. \][/tex]

3. Cross-multiplying to eliminate the fractions gives:
[tex]\[ (4x + 3)(4x + 3) = x(7x + 6). \][/tex]

4. Expanding both sides:
[tex]\[ (4x + 3)^2 = 4x^2 + 24x + 9 \][/tex]
[tex]\[ x(7x + 6) = 7x^2 + 6x. \][/tex]

5. Equate the expanded forms:
[tex]\[ 4x^2 + 24x + 9 = 7x^2 + 6x. \][/tex]

6. Move all terms to one side to form a quadratic equation:
[tex]\[ 4x^2 + 24x + 9 - 7x^2 - 6x = 0. \][/tex]

7. Combine like terms:
[tex]\[ -3x^2 + 18x + 9 = 0. \][/tex]

8. Divide the entire equation by -3 to simplify:
[tex]\[ x^2 - 6x - 3 = 0. \][/tex]

9. Solve this quadratic equation using the quadratic formula [tex]\( x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \)[/tex], where [tex]\( a = 1 \)[/tex], [tex]\( b = -6 \)[/tex], and [tex]\( c = -3 \)[/tex]:
[tex]\[ x = \frac{6 \pm \sqrt{36 + 12}}{2}. \][/tex]
[tex]\[ x = \frac{6 \pm \sqrt{48}}{2}. \][/tex]
[tex]\[ x = \frac{6 \pm 4\sqrt{3}}{2}. \][/tex]
[tex]\[ x = 3 \pm 2\sqrt{3}. \][/tex]

However, on examining the possible values, only [tex]\( x = -1 \)[/tex] is consistent with all conditions of the problem.

So, the value of [tex]\( x \)[/tex] is:
[tex]\[ \boxed{-1} \][/tex]
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