Question:
Write the value of x for which 2x, x + 10 and 3x + 2 are in A.P.
Solution:
Here, we are given three terms,
First term $\left(a_{1}\right)=2 x$
Second term $\left(a_{2}\right)=x+10$
Third term $\left(a_{3}\right)=3 x+2$
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,
$d=a_{2}-a_{1}$
$d=(x+10)-(2 x)$
$d=x+10-2 x$
$d=10-x$ $\ldots(1)$
Also,
$d=a_{3}-a_{2}$
$d=(3 x+2)-(x+10)$
$d=3 x+2-x-10$
$d=2 x-8$$\ldots(2)$
Now, on equating (1) and (2), we get,
$10-x=2 x-8$
$2 x+x=10+8$
$3 x=18$
$x=\frac{18}{3}$
$x=6$
Therefore, for $x=6$, these three terms will form an A.P.