Find the value of p and q in the arithmetic progression 2,p,q,8

1 answer

In an arithmetic progression (AP), the difference between consecutive terms is constant. Let's denote the common difference as \(d\).

Given the terms of the AP: \(2, p, q, 8\), we can express the conditions for the arithmetic progression:

  1. The difference between the second term \(p\) and the first term \(2\) should equal the difference between the third term \(q\) and the second term \(p\): \[ p - 2 = d \]

  2. The difference between the third term \(q\) and the second term \(p\) should equal the difference between the fourth term \(8\) and the third term \(q\): \[ q - p = d \] \[ 8 - q = d \]

Since \(p - 2 = d\), we can substitute \(d\) in the second equation: \[ q - p = p - 2 \]

Rearranging gives: \[ q = 2p - 2 \]

Now substituting \(d\) in the third equation: \[ 8 - q = p - 2 \]

Substituting \(q\) from the earlier equation: \[ 8 - (2p - 2) = p - 2 \] \[ 8 - 2p + 2 = p - 2 \] \[ 10 - 2p = p - 2 \]

Now, rearranging this equation: \[ 10 + 2 = p + 2p \] \[ 12 = 3p \] \[ p = 4 \]

Now that we have \(p\), we can find \(q\): \[ q = 2p - 2 = 2(4) - 2 = 8 - 2 = 6 \]

Thus, the values are: \[ p = 4, \quad q = 6 \]

To confirm, the terms of the arithmetic progression are \(2, 4, 6, 8\) and the common difference \(d\) is: \[ 4 - 2 = 2, \quad 6 - 4 = 2, \quad 8 - 6 = 2 \]

The common difference is consistent. Hence, the final answer is: \[ p = 4, \quad q = 6 \]