Answer:
[tex]\frac{21}{2}[/tex]
Step-by-step explanation:
Given
a₁ = 6
a₂ = 12 , then
a₃ = [tex]\frac{6+12}{2}[/tex] = [tex]\frac{18}{2}[/tex] = 9 ← an integer
a₄ = [tex]\frac{12+9}{2}[/tex] = [tex]\frac{21}{2}[/tex] ← not an integer
Thus the fourth term is not an integer