Question:
Find the value of x for which (8x + 4), (6x − 2) and (2x + 7) are in A.P.
Solution:
Here, we are given three terms,
First term $\left(a_{1}\right)=8 x+4$
Second term $\left(a_{2}\right)=6 x-2$
Third term $\left(a_{3}\right)=2 x+7$
We need to find the value of x for which these terms are in A.P. So, in an A.P. the difference of two adjacent terms is always constant. So, we get,
$d=a_{2}-a_{1}$
$d=(6 x-2)-(8 x+4)$
$d=6 x-8 x-2-4$
$d=-2 x-6 \ldots \ldots(1)$
Also,
$d=a_{3}-a_{2}$
$d=(2 x+7)-(6 x-2)$
$d=2 x-6 x+7+2$
$d=-4 x+9 \ldots \ldots(2)$
Now, on equating (1) and (2), we get,
$-2 x-6=-4 x+9$
$4 x-2 x=9+6$
$2 x=15$
$x=\frac{15}{2}$
Therefore, for $\left.x=\frac{15}{2}\right]$, these three terms will form an A.P.