Question

Solve it fast please I'm very excited about this

Answer 1

Tn=-13/2
t2=31/4
t31=1/2
31/4=a+d=>31-4d/4=a
1/2=a+30d
1-60d/2=a
equating a we get
31-4d/4=1-60d/2
31-4d=2-120d
29=-116d
d=116/29
d=4
so 1/2=a+30*4
1/2=a+120
so a=1-240/2
a=-239/2
so -13/2=-239/2+(n-1)4
226/2=(n-1)4
113=n