nhanh nha chieu mk phai nop rui
b1 tính tổng
a,A=1+4+7+....+601
b,B=1+5+9+...+801
c,C=3+8+13+...+903
b2 so sánh
a,A=200.200;B=190.210
b,A=402.402,B=400.404
*chú ý:dấu chấm là dấu nhân nha
hy vọng các bạn sẽ giúp mk
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b1
a) \(\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}+\dfrac{1}{8.9}+\dfrac{1}{9.10}\)
\(=\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{10}\)
\(=\dfrac{1}{5}-\dfrac{1}{10}\)
\(=\dfrac{2}{10}-\dfrac{1}{10}\)
\(=\dfrac{1}{10}\)
b) \(\dfrac{1}{1.2}+\dfrac{1}{2.3}+...+\dfrac{1}{99.100}\)
\(=\dfrac{1}{1}-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{99}-\dfrac{1}{100}\)
\(=\dfrac{1}{1}-\dfrac{1}{100}\)
\(=\dfrac{99}{100}\)
c) \(\dfrac{2}{3.5}+\dfrac{2}{5.7}+\dfrac{2}{7.9}+\dfrac{2}{9.11}\)
\(=\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11}\)
\(=\dfrac{1}{3}-\dfrac{1}{11}\)
\(=\dfrac{8}{33}\)
d) \(\dfrac{2}{3.5}+\dfrac{2}{5.7}+...+\dfrac{2}{99.101}\)
\(=\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{99}-\dfrac{1}{101}\)
\(=\dfrac{1}{3}-\dfrac{1}{101}\)
\(=\dfrac{98}{303}\)
a) 2n + 1 \(⋮\)n - 5
=> 2.( n - 5 ) + 1 + 10 \(⋮\)n - 5
=> 2.( n - 5 ) + 11 \(⋮\)n - 5
=> 11 \(⋮\)n - 5 [ vì 2.( n - 5 ) \(⋮\)n - 5 ]
=> n - 5 \(\in\)Ư(11) = { -11 ;- 1;1 ; 11 }
=> n \(\in\){ -6; 4;6;16 }
Vậy: n \(\in\){ -6; 4;6;16 }
b) n2 + 3n - 13 \(⋮\)n + 3
=> n.n + 3n - 13 \(⋮\)n + 3
=> n.( n+ 3 ) + 3 . ( n + 3 ) - 13 - 3n - 9 \(⋮\)n + 3
=> 13 - 3n - 9 \(⋮\)n + 3 [ vì n.( n + 3 ) và 3.( n + 3 ) \(⋮\)n + 3 ]
=> 3n - 22 \(⋮\)n + 3
=>3.( n - 3 ) - 22 - 9 \(⋮\)n + 3
=> 3.( n - 3 ) - 31 \(⋮\)n + 3
=> 31 \(⋮\)n + 3 [ vì 3. ( n - 3 ) \(⋮\)n + 3 ]
=> n + 3 \(\in\)Ư ( 31 ) = { -31 ; -1 ; 1 ; 31 }
=> n \(\in\){ -34 ; -4; -2 ; 28 }
Vậy: n \(\in\){ -34 ; -4; -2 ; 28 }
c) n2 + 3 \(⋮\) n - 1
=> n.n + 3 \(⋮\) n - 1
=> n.( n - 1 ) + 3 - n \(⋮\) n - 1
=> 3 - n \(⋮\) n - 1 [ vì n.( n - 1 ) \(⋮\) n - 1 ]
=> n - 3 \(⋮\) n - 1
=> ( n - 1 ) - 2 \(⋮\) n - 1
=> n - 1 \(\in\)Ư( 2 )= { -2 ; - 1; 1 ; 2 }
=> n \(\in\){ -1 ; 0 ;2 ;3 }
vậy: n \(\in\){ -1 ; 0 ;2 ;3 }
Bài 5:
a: =1/3+2/5
=5/15+6/15
=11/15
b: =6/21+12/21=18/21=6/7
c: =16/24+10/24
=26/24
=13/12
d: =4/12+3/12+10/12
=17/12
e: =19/24-9/24
=10/24
=5/12
f: =8/9-3/9=5/9
g: =9/3+1/3=10/3
k: =15/24+42/24+14/24
=71/24
Bài 1:
a: -8/12<0<-3/-4
b: -56/24<0<7/3
c: 4/25<1<15/13
=>-4/25>-15/13
Bài 2:
a: =-60/45=-4/3
b: =4/15-3/2-8/5=8/30-45/30-48/30=-85/30=-17/6
\(A=1+2+3+...+7+8=\dfrac{\left(8+1\right).\left(\dfrac{8-1}{1}+1\right)}{2}=36\)
\(B=3+4+5+...+10+11=\dfrac{\left(11+3\right).\left(\dfrac{11-3}{1}+1\right)}{2}=63\)
\(C=1+3+5+...+13+15=\dfrac{\left(15+1\right).\left(\dfrac{15-1}{2}+1\right)}{2}=64\)
\(D=2+4+6+...+18+20=\dfrac{\left(20+2\right).\left(\dfrac{20-2}{2}+1\right)}{2}=110\)
\(E=1+4+7+...+22+25=\dfrac{\left(25+1\right).\left(\dfrac{25-1}{3}+1\right)}{2}=117\)
\(G=1+5+9+...+33+37+41=\dfrac{\left(41+1\right).\left(\dfrac{41-1}{4}+1\right)}{2}=231\)
các bạn ơi giúp nha năn nỉ đó
k mk đi
ai k mk
mk k lại
thanks