nếu
1+4=5
2+5=12
3+6=21
8+11 = ?
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1 + 4 = 5
2 + 5 = 12 ( 2 + 5 + 5 = 12)
3 + 6 = 21 (3 + 6 + 12 = 21)
8 + 11 = 40 ( 8 + 11 + 21= 40)
Quy luật Cộng thêm kết quả của dãy số ở trên
g: \(=-457+237+23-123=-220-100=-320\)
h: \(=\left(1-3\right)+\left(5-7\right)+...+\left(41-43\right)+\left(45-47\right)\)
\(=\left(-2\right)+\left(-2\right)+...+\left(-2\right)+\left(-2\right)\)
\(=-2\cdot12=-24\)
i: \(=173+27-46-54-19=200-100-19=100-19=81\)
k: \(=-52+82+49-15+13-36\)
\(=30+34-23\)
=30+11
=41
l: \(=\left(3-5\right)+\left(7-9\right)+\left(11-13\right)+\left(15-17\right)\)
\(=\left(-2\right)+\left(-2\right)+\left(-2\right)+\left(-2\right)\)
=-8
m: \(=\left(1-2\right)+\left(3-4\right)+...+\left(2001-2002\right)+2003\)
\(=2003-1-1-...-1\)
\(=2003-1001=1002\)
n:Số số hạng là:
\(\left[\left(-51\right)-\left(-99\right)\right]:1+1=49\left(số\right)\)
Tổng là \(\left(-51-99\right)\cdot\dfrac{49}{2}=-3675\)
o: \(=-62-38+1523-2523-92\)
\(=-100+1000-92=900-92=808\)
a) \(\left(-48\right)+127+\left(-52\right)+73\)
\(=\left(-48-52\right)+\left(127+73\right)\)
\(=-100+200\)
\(=100\)
b) \(\left(-38\right)\cdot45+\left(-38\right)\cdot55\)
\(=\left(-38\right)\cdot\left(45+55\right)\)
\(=\left(-38\right)\cdot100\)
\(=-3800\)
c) \(\left(-125\right)+371+\left(-875\right)+629+150\)
\(=\left(-125-875\right)+\left(371+629\right)+150\)
\(=-1000+1000+150\)
\(=150\)
d) \(271+\left(-392\right)+729+\left(-608\right)+\left(-123\right)\)
\(=\left(271+729\right)+\left(-392-608\right)-123\)
\(=1000-1000-123\)
\(=-123\)
e) \(\left(-48\right)\cdot25+25\cdot\left(-52\right)\)
\(=25\cdot\left(-48-52\right)\)
\(=25\cdot-100\)
\(=-2500\)
f) \(47\cdot\left(-11\right)+47\)
\(=47\cdot\left(-11+1\right)\)
\(=47\cdot-10\)
\(=-470\)
g) \(56-7\cdot8+11\)
\(=56-56+11\)
\(=0+11\)
\(=11\)
h) \(-42+51+2+\left(-11\right)+40\)
\(=\left(-42+2\right)+\left(51-11\right)+40\)
\(=-40+40+40\)
\(=0+40\)
\(=40\)
a: =-48-52+127+73
=200-100
=100
b; \(=-38\left(45+55\right)=-38\cdot100=-3800\)
c: \(=-125-875+371+629+150\)
=-1000+1000+150
=150
d: =271+729-392-608-123
=1000-1000-123
=-123
e: =25(-48-52)
=25*(-100)
=-2500
f: =47(-11+1)
=47(-10)
=-470
g: =56-56+11
=11
h: =-42+2+51-11+40
=-40+40+40
=40
a: =6/35x39/54=13/105
b: \(=\dfrac{-5}{7}\left(\dfrac{2}{11}+\dfrac{9}{11}\right)+\dfrac{12}{7}=\dfrac{-5}{7}+\dfrac{12}{7}=1\)
Bài 1:
a: \(x=\dfrac{2}{3}:\dfrac{3}{5}=\dfrac{2}{3}\cdot\dfrac{5}{3}=\dfrac{10}{9}\)
b: \(x=\dfrac{17}{8}:\dfrac{7}{17}=\dfrac{17}{8}\cdot\dfrac{17}{7}=\dfrac{289}{56}\)
c: \(x=-\dfrac{3}{4}:\dfrac{7}{12}=\dfrac{-3}{4}\cdot\dfrac{12}{7}=\dfrac{-63}{28}=-\dfrac{9}{4}\)
d: \(\Leftrightarrow x\cdot\dfrac{1}{6}=\dfrac{3}{8}-\dfrac{1}{4}=\dfrac{1}{4}\)
hay \(x=\dfrac{1}{4}:\dfrac{1}{6}=\dfrac{3}{2}\)
e: \(\Leftrightarrow\dfrac{1}{2}:x=-4-\dfrac{1}{3}=-\dfrac{17}{3}\)
hay \(x=-\dfrac{1}{2}:\dfrac{17}{3}=\dfrac{-3}{34}\)
\(B=\frac{1}{1\cdot2\cdot3}+\frac{1}{2\cdot3\cdot4}+\frac{1}{3\cdot4\cdot5}+\frac{1}{18\cdot19\cdot20}\)
\(B=\frac{1}{2}\left(\frac{2}{1\cdot2\cdot3}+\frac{2}{2\cdot3\cdot4}+\frac{2}{3\cdot4\cdot5}+\frac{2}{18\cdot19\cdot20}\right)\)
\(B=\frac{1}{2}\left(\frac{1}{1\cdot2}-\frac{1}{2\cdot3}+\frac{1}{2\cdot3}-\frac{1}{3\cdot4}+\frac{1}{3\cdot4}-\frac{1}{4\cdot5}+...+\frac{1}{18\cdot19}-\frac{1}{19\cdot20}\right)\)
\(B=\frac{1}{2}\left(\frac{1}{1\cdot2}-\frac{1}{19\cdot20}\right)\)
\(B=\frac{1}{2}\cdot\frac{189}{380}=\frac{189}{760}\)
\(C=\frac{52}{1\cdot6}+\frac{52}{6\cdot11}+\frac{52}{11\cdot16}+...+\frac{52}{31\cdot36}\)
\(C=\frac{52}{5}\left(\frac{5}{1\cdot6}+\frac{5}{6\cdot11}+\frac{5}{11\cdot16}+...+\frac{6}{31\cdot36}\right)\)
\(C=\frac{52}{5}\left(1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+\frac{1}{11}-\frac{1}{16}+...+\frac{1}{31}-\frac{1}{36}\right)\)
\(C=\frac{52}{5}\cdot\left(1-\frac{1}{36}\right)\)
\(C=\frac{91}{9}\)
a: =>3/8x6/3<x<20/21x21/4
=>3/4<x<5
hay \(x\in\left\{1;2;3;4\right\}\)
b: =>56/42<x<11/2
=>4/3<x<11/2
nên \(x\in\left\{2;3;4;5\right\}\)
1+4=5
2+5=12
3+6=21
Ta thấy: 1x4+1=5
2x5+2=12
3x6+3=21
...
=>8x11+8=96
Vậy KQ cuối cùng là 96
K mình nhá
8+11=19