Tính tổng :
\(\eqalign{ & a)\;S = 1 + 2 + 3 + ... + 100 \cr & b)\;S = 15 + 17 + 19 + 21 + ... + 153 + 155 \cr & c)\;S = 4.325.6 + 4.69.24 + 3.339.8 \cr & d)\;S = 43.37 + 43.73 + 57.66 + 57.44 \cr & e)\;S = 48.19 + 48.115 + 134.52. \cr} \)
a) \(S = 1 + 2 + 3 + … + 100\)
\(= (1 + 100) + (2 + 99) + …+ (50 + 51)\)
\( = \underbrace {101 + 101 + ... + 101}_\text{có 50 số hạng101}\)
\(= 101.50\)
\(=5050\)
b) \(S = 15 + 17 + 19 + 21 + …+ 153 + 155\)
\(= (15 + 155) + (17 + 153) + …+ (83 + 87) + 85\)
\( = \underbrace {170 + 170 + ... + 170}_\text{có 35 số hạng 170} + 85 = 170.35 + 85\)
\(= 5950 + 85\)
\(= 6035\)
c) \(S = 4.325.6 + 4.69.24 + 3.399.8\)
\(= 24.325 + 24.69.4 + 24.399\)
\(= 24.(325 + 69.4 + 399)\)
\(= 24.1000 = 24000\)
d) \(S = 43.37 + 43.73 + 57.66 + 57.44\)
\(= 43.(37 + 73) + 57.(66 + 44)\)
\(= 43.110 + 57.110\)
\(= 110.(43 + 57)\)
\(= 110.100 = 11000\)
e) \(S = 48.19 + 48.115 + 134.52\)
\(= 48.(19 + 115) + 134.52\)
\(= 48.134 + 134.52\)
\(= 134.(48 + 52)\)
\(= 134.100 = 13400\)