Answer:
The first three terms in the geometric sequence are 18, 24, 32.
Step-by-step explanation:
A number when added to [tex]x,y,z[/tex] that yields consecutive terms of a geometric sequence is an unknown number [tex]t\in \mathbb{Z}[/tex]
Given
[tex]x = 1, y = 7, z = 15[/tex]
We know
[tex]\alpha _1 = 1+t[/tex]
[tex]\alpha _2 = 7+t[/tex]
[tex]\alpha _3 = 15+t[/tex]
Recall that a geometric sequence is in the form
[tex]\boxed{a_n = a_1 \cdot r^{n-1}}[/tex]
Therefore, once [tex]\alpha_1, \alpha_2, \alpha_1[/tex] are consecutive terms,
[tex]15+t = (1+t) r^{3-1} \implies 15+t = (1+t) r^2[/tex]
To find the ratio, for
[tex]\dots a_{k-1}, a_k, a_{k+1} \dots[/tex]
we know
[tex]\dfrac{a_k}{a_{k-1}} =\dfrac{a_k}{a_{k-1}} =r[/tex]
Therefore,
[tex]\dfrac{(7+t)}{(1+t)} =\dfrac{(15+t)}{(7+t)} \implies (7+t)^2 = (15+t)(1+t)[/tex]
[tex]\implies 49+14t+t^2=15+16t+t^2 \implies -2t=-34 \implies t=17[/tex]
The ratio is therefore
[tex]r=\dfrac{4}{3}[/tex]
Therefore, the first three terms in the geometric sequence are 18, 24, 32.
