(1×19) + (2×19) + (3×19) + ... + (19×19) = ... ( pakai cara ya)

U1= 1x19= 19
U2= 2x19= 38
U3= 3x19= 57

Beda = U2-U1= 38-19= 19

U19= 19 x 19
= 361

Sn = n/2 x (U1+Un)
S19= 19/2 x (19+361)
= 19/2 x 380
= 19 x 190
= 3.610