Answer:
a₁₅ = 240
55 is not term in the sequence
Step-by-step explanation:
[tex]n(n+1)=240\\\\n^2+n-240=0\\\\n=\dfrac{-1\pm\sqrt{1-4(-240)}}{2}=\dfrac{-1\pm\sqrt{1+960}}{2}=\dfrac{-1\pm31}{2}\quad\wedge\quad n\in N_+\\\\n=15[/tex]
if n is even number then (n+1) is odd number and if n is odd number then (n+1) is even number
The product of numbers where one of them is even will always be even.
55 is odd number so it is not term of this sequence.
