Tính A = 1.3 + 3.5 + 5.7 + … + 31.33
Giải thích
A = 1.3 + 3.5 + 5.7 + … + 31.33
6A = 1.3.6 + 3.5.6 + 5.7.6 + … + 31.33.6
6A = 1.3(5 + 1) + 3.5(7 – 1) + … + 31.33.(35 – 29)
6A = 1.3.5 + 1.3 + 3.5.7 – 1.3.5 + 5.7.9 – 3.5.7 + … + 31.33.35 – 29.31.33
6A = 1.3 + 31.33.35
6A = 3 + 35805
6A = 35808
A = \(\frac{{11935}}{2}\)