Sn=1/2 n(3n-1) maka u10=

sn=1/2 10(3.10-1)
1/2 10 (29)
1/2 .290=145

sn = 1/2 n (3n-1)

s1 = a = 1/2 (3-1) = 1/2 (2) = 1
s2 = a+b = 1/2 × 2 (6-1) = 5

a = 1
a+b = 5
1+b = 5
b = 4

u10 = a+9b
u10 = 1 + 36
u10 = 37