Jawabanmu

2014-03-18T18:59:26+07:00
Misal : banyak orang = n
banyak jabat tangan = (n × (n-1)) ÷ 2
= (10 ×9) ÷ 2
= 45
2014-03-18T19:09:53+07:00
>>1+2+3+4...+(10-1)
>>1+2+3+4...+9
>>(9+1)+ (8+2)...(4+6)+5
>>10(4) +5
45