Given: a₂ = 13

a₅ = 25

To find: a₁₇

Consider a₂ = 13

⇒ a + d = 13 …………….(1)

Consider a₅ = 25

⇒ a + 4d = 25 …………….(2)

Subtracting equation (1) from equation (2), we get,

3d = 12

⇒ d = 4

∴ Common difference = 4

From equation (1), we get

a = 13 - d

= 13 - 4

= 9

Thus a₁₇ = a + 16d

= 9 + 16(4)

= 73