\(\frac{1}{4}+\frac{1}{12}+\frac{1}{24}+\frac{1}{40}+\frac{1}{60}+\frac{1}{84}=\frac{12}{7}\)
TK MK NHA CÁC BẠN MK ĐG BỊ ÂM ĐIỂM
đặt A =1/4+...+1/84
A=2/8 +2/24+...+2/168
A=2/2.4+2/4.6+...+2/12.14
A=1/2-1/4+1/4-1/6 +...+1/12-1/14
A=1/2-1/14
A=6/14=3/7
\(\frac{1}{4}+\frac{1}{12}+\frac{1}{24}+\frac{1}{40}+\frac{1}{60}+\frac{1}{84}\)
\(=\left(\frac{1}{4}+\frac{1}{12}\right)+\left(\frac{1}{24}+\frac{1}{40}\right)+\left(\frac{1}{60}+\frac{1}{84}\right)\)
\(=\frac{1}{3}+\frac{1}{15}+\frac{1}{35}=\frac{3}{7}\)
