bai 1:
a,1/6+1/20+1/30+1/42+1/56+1/72=?
tim x
b,575--[6x+70]=445
c,315+[125-x]=435
giai giup minh nhe^_^
Giai giup minh bai toan tinh nhanh nay nhe
a) 7/4+7/28+7/70+7/130
b) 99/98-98/97+1/97×98
c) 51×115+37×102-17×45-37×2
d) 10+1/90-1/72-1/56-1/42-1/30-1/20-1/6-1/2
a)=7x(1/4+1/28+1/70+1/130)
=7x(1/1x4+1/4x7+1/7x10+1/10x13)
=7x(1-1/4+1/4-1/7+1/7-1/10+1/10-1/13)
=7x(1+1/13)
=7x14/13=98/13
Các câu còn lại p dựa theo cách trên làm nốt nhé!!!
Tinh tong:
S1=1/2+ 1/6+ 1/12+ 1/20 + 1/30 + 1/42 + 1/56+ 1/72 +1/90.
Giup mk vs nhe ,mk se tick.
\(S1=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\)
\(S1=\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+\frac{1}{7\cdot8}+\frac{1}{8\cdot9}+\frac{1}{9\cdot10}\)
\(S1=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\)
\(S1=1-\frac{1}{10}\)
\(S1=\frac{9}{10}\)
CHÚC BN HC GIỎI !!!!!!!!!! TỨ DIỆP THẢO
S=\(\frac{1}{1.2}+\frac{1}{2.3}+...............+\frac{1}{9.10}\)
=\(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...............+\frac{1}{9}-\frac{1}{10}\)
=\(1-\frac{1}{10}\)
=\(\frac{9}{10}\)
A=1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72
Ai nhanh nhat minh se tik cho nha nhan len nhe
A=1/2+1/6+....+1/56+1/72
A=1/1.2+1/2.3+...+1/7.8+1/8.9
A=1/1-1/2+1/2-1/3+...+1/7-1/8+1/8-1/9
A=1/1-1/9=9/9-1/9=8/9
A=\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+..\frac{1}{8.9}\)
A=\(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+..+\frac{1}{8}-\frac{1}{9}\)
A=1-\(\frac{1}{9}\)=\(\frac{8}{9}\)
giup to bai nay voi
1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/110+1/132
1/3-1/12
=1/4
Chúc bạn bạn may mắn!
1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90 + 1/110 + 1/132 = 2/3,
Đúng 100%!
Ai tk cho mình mình tk lại.
Bai 1:Chung minh rang:A=1/42+1/62+1/82+.......+1/(2n)2<1/4
Bai 2:Tinh tong:1/2+5/6+11/12+19/20+41/42+55/56
cac ban giup minh nha.trinh bay theo kieu phan so nhe
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90
cac ban giup mik voi
\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\)
\(=\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+\frac{1}{5\times6}+\frac{1}{6\times7}+\frac{1}{7\times8}+\frac{1}{8\times9}+\frac{1}{9\times10}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}\)
\(+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\)
( Gạch bỏ các phân số giống nhau )
\(=1-\frac{1}{10}\)
\(=\frac{9}{10}\)
Chúc bn học tốt !!!!
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90
=1/1x2+1/2x3+1/3x4+1/4x5+1/5x6+1/6x7+1/7x8+1/8x9+1/9x10
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10
=1-1/10
=9/10
k đúng cho mk nh!!!
1/2+1/6+1/12+1/20+1/30+1/x=41/42
giai giup minh cau nay nhe
\(\frac{1}{x}=\frac{41}{42}-\frac{1}{30}-\frac{1}{20}-\frac{1}{12}-\frac{1}{6}-\frac{1}{2}\)
\(\frac{1}{x}=\frac{1}{7}\). Suy ra \(x\)= 7.
1/2 +1/6 +1/12+1/20+1/30+1/x=41/42
Ta có \(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}=\frac{41}{42}\)
mà 6 . 7 bàng 42=> x=42
mà . là dấu nhân
Tính: B=1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72
A=1/90-1/72-1/56-1/42-1/30-1/20-1/12-1/6-1/2
em lớp 6 nha
B= 1/2 + 1/6 + 1/12 +1/20 + 1/30 + 1/42 + 1/56 + 1/72
B= 1/1*2 + 1/2*3 + 1/3*4 + 1/4*5 + 1/5*6 + 1/6*7 + 1/7*8 + 1/8*9
B=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
B=1+0-0-0-0-0-0-0-1/9
B=1-1/9
B=8/9
k em nha
a/(x-15)-75=0
b/575-(6x+70)=445
c/315+(125-x)=435
d/x-105:21=15
e/(x-105):21=1
a) ( x - 15 ) - 75 = 0
x - 15 = 75
x = 75 + 15
x = 90
Vậy x = 90
b) 575 - ( 6x + 70 ) = 445
6x + 70 = 575 - 445
6x + 70 = 130
6x = 60
x = 10
Vậy x = 10
c) 315 + ( 125 - x ) = 435
125 - x = 120
x = 125 - 120
x = 5
Vậy x = 5
d) x - 105 : 21 = 15
x - 5 = 15
x = 20
Vậy x = 20
e) ( x - 105 ) : 21 = 1
x - 105 = 21
x = 21 + 105
x = 126
Vậy x = 126
a) (x-15)-75=0
x-15 = 0+75
x-15 = 75
x = 75 + 15
x = 90
b) 575-(6x+70)=445
6x+70 = 575-445
6x+70 = 130
6x = 130 - 70
6x = 60
x = 60:6
x = 10
d) x-105:21 = 15
x-105 = 15.21
x-105 = 315
x = 315 + 105
x = 420
e) (x-105):21 = 1
=> x-105 = 21
x = 105 + 21
x = 126
Tìm x:
a) ( x - 15 ) - 75 = 0 c) 315 + ( 125 - x ) = 435
x - 15 = 75 + 0 125 - x = 435 - 315
x - 15 = 75 125 - x = 120
x = 75 + 15 x = 125 - 120
x = 90 x = 5
b) 575 - ( 6x + 70 ) = 445 d) x - 105 : 21 = 15
6x + 70 = 575 - 445 x - 105 = 15 x 21
6x + 70 = 130 x - 105 = 315
6x = 130 - 70 x = 315 + 105
6x = 60 x = 420
x = 60 : 6
x = 10