a. ta có
A=5²/1.6+5²/6.11+...+5²/26.33
A= 5. (5/1.6+5/6.11+...+5/26.33)
A=5.(1-1/6+1/6-1/11+...+1/26-1/33)
A=5.(1-1/33)
A=5.32/33
A=160/33
a.ta có:
A=2/1.3+2/3.5+...+2/99.101
A=(1-1/3+1/3-1/5+...+1/99-1/101)
A=(1-1/101)
A=100/101
a.ta có:
A=1/5.6+1/6.7+1/7.8+...+1/24.25
A=(1/5-1/6+1/6-1/7+1/7-1/8+...+1/24-1/25)
A=(1/5-1/25)
A=4/25
a.ta có:
A=3/1.4+3/4.7+3/7.11+3/11.14+3/14.17
A=(1-1/4+1/4-1/7+1/7-1/11+1/11-1/14+1/14-1/17)
A=(1-1/17)
A=16/17
b.ta có:
B=1/7+1/91+1/247+1/475+1/775+1/1147
B=1/1.7+1/7.13+1/13.19+1/19.25+1/25.31+1/31.37
B=1/6(1-1/7+1/7-1/13+1/13-1/19+1/19-1/25+1/25-1/31+1/31-1/37)
B=1/6(1-1/37)
B=1/6.36/37
B=6/37
b.ta có:
B=1/2+1/6+1/12+1/20+1/30
B=1/1.2+1/2.3+1/3.4+1/4.5+1/5.6
B=(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6)
B=(1-1/6)
B=5/6
b.ta có:
B=1/15+1/35+1/63+1/99+1/143
B=1/3.5+1/5.7+1/7.9+1/9.11+1/11.13
B=1/2(1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13)
B=1/2(1-1/13)
B=1/2.12/13
B=3/7
còn mấy phần bạn tự làm nốt nha giờ mình đi ngủ đây!sorry nha!
