Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
2.17.12+4.6.21+62.8.3
= 2.12.17 + 24.12+62.24
= 24.17+24.12+62.24
Đến đây thì bn biết rồi đk.k nha
2.17.12 + 4.6.21 + 62.8.3
= 24.17 + 24.21 + 24 . 62
= 24. (17 + 21 + 62)
= 24 . 100
= 2400
Số các số hạng là:
(1995-1):2+1=998 (số)
Tổng của dãy số trên là:
(1995+1)x998:2=996004
Đáp số: 996004.
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
<=> 1/3 + 1/6 + 1/10 +...+ 1/x(x+1):2 = 1/1991/1993 - 1 = 1991/1993
<=> 1/2(2+1):2 + 1/3(3+1):2 + ...+ 1/x(x+1):2 = 1991/1993
<=> 1/2.3:2 + 1/3.4:2 +...+ 1/x(x+1):2 = 1991/1993
<=>(1/2 - 1/3):1/2 + (1/3 - 1/4 ):1/2+...+(1/x-1/x+1):1/2=1991/1993
<=>(1/2-1/3).2 + (1/3-1/4).2+...+(1/x-1/x+1).2 = 1991/1993
<=>2.(1/2-1/3+1/3-1/4+1/4-1/5+....+1/x-1/x+1)=1991/1993
<=>2.(1/2-1/x+1)=1991/1993
<=>1/2-1/x+1=1991/1993:2=1991/3986
<=> 1/x+1=1/2-1991/3986=2/3986=1/1993
=>x=1993-1=1992
ừm khó phết mặc dù mình là học sinh lớp 6
để nghĩ cái
à ừ......................
lúc nào bùi đức thắng cx nói câu đấy nghe phát ngán
s= (2/1.2.3 +2/2.3.4+...+2/98.99.100):2= (1/1.2-1/2.3+1/2.3-1/3.4+...+1/98.99-1/99.100):2=(1/1.2-1/99.100):2=4949/19800=>S=4949/19800
Có (x-1) + (x-2) + ...+ (x-99) = 99x - 1
<=> x-1 + x-2 + ... + x-99 = 99x - 1
(x + x + ... + x) - (1+2+...+99) = 99x - 1
99x - 4950 = 99x - 1 (loại)
Vậy x thuộc tập hợp rỗng
Theo mình nghĩ
(4+3) - 2 =5
(8+6) - 4 =10
(3+1) - 2 = 2
=> (6+2) - 4 =4
k giải đc
nhiều số quá