5+7+9+11+13+15+17+19+21+23+25+27+29+31+33+35+37+39+41+43+45+47+49+51+53+55+57+59+61+63+65+67+69+71+73+75+77+79+81+83+85+87+89+91+93+95+97+99+101+103+105+107+109

Matematika
Pola Bilangan VII SMP

Pembahasan :
Un = 121
a + (n - 1)b = 121
5 + (n - 1)2 = 121
5 + 2n - 2 = 121
2n + 3 = 121
2n = 118
n = 59

5 + 7 + 9 + ... + 121
= S59
= 59/2(5 + 121)
= 59/2(126)
= 3717