Cho A=\(\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{100^2}\\ CMRA< \frac{3}{4}\)
CMR: 1/26 +1 /27 + ... + 1/50 = 99/50 - 97/50 +...+ 7/4 - 5/3 + 3/2 - 1
1/1*2*3*4+1/2*3*4*5+1/3*4*5*6+...+1/47*48*49*
50
1/1*2 + 1/2*3 + 1/3*4 + 1/4*5 + ... +1/49*50
tính các tổng sau
A=1*2+2*3+3*4+4*5+5*6+6*7...+49*50
B=1*50+2*49+3*48+...+49*2+50*1
1/2×3+1/2×3×4+1/3×4×5+...+1/48×49×50
Chứng minh 1/2+1/3×4+1/5×6+...+1/49×50=1/26+1/27+....+1/50
1/1*2+1/3*4+1/5*6+...+1/49*50=1/26+1/27+1/28+...+1/50
1/1×2+1/2×3+1/3×4+1/4×5+...+1/49×50
