tính các tổng sau: S1=1+2+3+….+999 S2=21+23+25+…+1001 S3=15+17+19+21+…+151+153+155 S4=24+25+26+…+125+126 S5=10+12++14+…+2010 S6=1+4+7+…+79

S1 = 1 + 2 + 3 + … + 999

S1 = ( 999 + 1 ) × 999 : 2 =

S1 = 499500

…

S2 = 21 + 23 + 25 + … + 1001

S2 = ( 1001 + 21 ) × 491 : 2 

S2 = 250901

…

S3 = 15 + 17 + 19 + 21 + … + 151 + 153 + 155

S3 = ( 155 + 15 ) × 71 : 2 

S3 = 6035

…

S4 = 24 + 25 + 26 + … + 125 + 126

S4 = ( 126 + 24 ) × 103 : 2 

S4 = 7725

…

S5 = 10 + 12 + 14 + … + 2010

S5 = ( 2010 + 10 ) × 1001 : 2

S5 = 1011010

…

S6 = 1 + 4 + 7 + …  + 79

S6 = ( 79 + 1 ) × 27 : 2

S6 = 1040

…

S7 = 15 + 25 + 35 + … + 115

S7 = ( 115 + 15 ) × 11 : 2

S7 = 715

`#cactus`

 

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