Vi sao 1 =100000000
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Câu này con thấy đc
1+1+2+2+3+3+....+100000000+100000000=2(1+2+3+...+100000000)=2x100000000x100000001:2=100000000x100000001
400000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
Đặt A = 1+2+3+4+...+100000000 (có 100000000 số hạng)
A = (1+100000000) x 100000000 : 2
A = 100000001 x 100000000 : 2
A = 10000001 x 50000000
A = 5000000500000000
Vậy 1+2+3+4+...+100000000 = 5000000500000000
từ 1 đến 100000000 có 100000000 số
tổng là:
100000000+1*100000000/2=5000000005000000
đ/s:5000000005000000
vì 100000000:1 =>1=100000000