In the following A.P., find the missing terms:

□, 13, □, 3

Given: a₂ = 13 and a₄ = 3

We know that,

a_n = a + (n – 1)d

a₂ = a + (2 – 1)d

13 = a + d …(i)

and a₄ = a +(4 – 1)d

3 = a + 3d …(ii)

Solving linear equations (i) and (ii), we get

a + d – a – 3d = 13 – 3

⇒ –2d = 10

⇒ d = –5

Putting the value of d in eq. (i), we get

a – 5 = 13

⇒ a = 18

Now, a₃ = a + 2d = 18 + 2(–5) = 18 – 10 = 8

Hence, the missing terms are 18 and 8