Solution :
First term (a) = √2
Common difference (d) = 3 √2 - √2 = 2 √2
n = 12
General term of an A.P
tn = a + (n - 1) d
t₁₂ = √2 + (12 - 1) (2√2)
= √2 + 11 (2√2)
= √2 + 22 √2
= 23 √2
Hence, 12th of A.P is 23 √2