Bài 1: Tính bằng cách hợp lí: c, 1+3+5+7+9+………..+2013 d, 1+2+3+4+…………….+n e, 100+98+96+……………………+2 – 97-95-…………

$\color{black}{c, 1+3+5+7+9+….+2013}$

$\color{black}{= 504.1007}$

$\color{black}{= 507528}$

$\color{black}{d, 1+2+3+4+….+n}$

$\color{black}{=[(n-1):1+1].[(n+1):2]}$  (dạng tổng quát)

$\color{black}{e, 100+98+96+….+2 – 97-95-….-1}$

$\color{black}{= 100+1.49}$

$\color{black}{= 149}$

$\color{black}{g, 2.3.12 + 4.6.42 = 8.27.3}$

$\color{black}{= 3^2.2^3+2^4.3^2.7+2^3+3^4}$