2(1+2+3+4+5........+100)=?

2(1+2+3+4+5........+100)=2 x 1/2(100)(1+100)
=10100//

1+到100
100+1=101
99+2=101
3+98=101
4=97=101
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.
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50+51=101
50x101=1+到100
(1+2+3+4+5........+100)=5050
5050x2=10100




一係你咁
((1+100)x100)/2=5050
2x5050=10100

2(1+2+3+4+5....+100)
=2 x (1+2+3+4+5..+100)
=2 x 10100
=20200

2 times 4950 =9900