tính nhanh
\(1.3+2.4+3.5+4.6+...+48.50+49.51\)
\(1.4+2.5+3.6+...+98.101+99.102\)
Những câu hỏi liên quan
Tính giá trị biểu thức :a,A=1.3+3.5+5.7+......+49.51
b, B=2.4+4.6+6.8+.....+48.50
c,C=1.3+2.4+3.5+4.6+......+10.12+11.13+12.14
d,D=1.4+4.7+7.10+....+46.49
giúp mình với ai nhanh mình tick cho
b: 6B=2*4*6+4*6*6+6*8*6+...+46*48*6+48*50*6
=2*4*6-2*4*6+4*6*8-4*6*8+...-44*46*48+46*48*50-46*48*50+48*50*52
=48*50*52
=>B=20800
d: 9D=1*4*9+4*7*9+...+46*49*9
=1*4*2+1*4*7-1*4*7+1*7*10-1*7*10+...+46*49*52-46*49*43
=1*2*4+46*49*52
=117216
=>D=13024
a: 
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tính:
A=1.3+2.4+3.5+...+99.101
B=1.4+2.5+3.6+...+99.102
tính nhanh
\(1.3+2.4+3.5+4.6+...+48.50+49.51\)
Tính tổng:
a) 1.2 + 2.3 + 3.4 + ... + 99.100
b) 1.3 + 2.4 + 3.5 + ... + 99.101
c) 1.4 + 2.5 + 3.6 + ... + 99.102
tính :
a. A = 1.4 + 2.5 + 3.6+...+ 99.102
b. B = 1.3+2.4+3.5 +...+99.101
c. C = 4 + 12 + 24 + 40 +...+ 19404 + 19800
\(A=1.\left(2+2\right)+2.\left(3+2\right)+3.\left(4+2\right)+....+99.\left(100+2\right)\)
\(A = (1.2 + 2.3 + 3.4 + ... + 99.100) + (1.2 + 2.2 + 3.2 + ... + 99.2)\)
\(Đặt B = 1.2 + 2.3 + 3.4 + ... + 99.100\)
\(3B = 1.2.(3-0) + 2.3.(4-1) + 3.4.(5-2) + ... + 99.100.(101-98)\)
\(3B = 1.2.3 - 0.1.2 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + ... + 99.100.101 - 98.99.100\)
\(3B = 99.100.101\)
\(B = 33.100.101 = 333300\)
\(A = 333300 + 2.(1 + 2 + 3 + ... + 99)\)
\(A = 333300 + 2.(1 + 99).99:2\)
\(A = 333300 + 100.99\)
\(A = 333300 + 9900\)
\(A = 343200\)
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a. A = 1.4 + 2.5 + 3.6 +...+ 99.102
= 1( 2 +2) + 2(3+2) +...+ 99 (100 +2)
= 1.2 + 1.2 +2.3 + 2.2 +...+ 99 .100 +99 . 2
= ( 1.2 +2.3 + 3.4 +...+99 . 100) + 2(1 + 2 + 3+...+99)
= 333300 + 9900 = 343 200
b. B = 1.3 + 2.4 + 3.5 +...+ 99.101
= 1(2 +1) + 2(3 +1) + 3(4 +1) +...+ 99(100 +1)
= 1.2 + 1 + 2.3 + 2 + 3.4 +...+ 99. 100 +99
= ( 1.2 + 2.3 + 3.4 +...+ 99.100) + (1+2+...+99)
= 333300 + 4950 = 338 250
c. C = 4 + 12 + 24 +...+ 19404 + 19800
1/2C = 1.2 + 2.3 + 3.4 +...+ 98.99 + 99.100
1/2 C = 333300
C = 333300 : 1/2 = 666600
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Tinh D=1.3+2.4+3.5+4.6+.....+99.100
E1.4+2.5+3.6+......+99.102
G=4+12+24+40+.....+19404+19800
tính nhanh
\(1.4+2.5+3.6+...+98.101+99.102\)
Ta có: A=1.4+2.5+3.6+.....+98.101+99.102
A=1.(2+2)+2.(3+2)+3(4+2)+........+98.(100+1)+99(100+2)
A=1.2+1.2+2.3+2.2+3.4+3.2+.........+98.100+98.1+99.100+99.2
A=(1.2+2.3+3.4+.......+99.100)+2.(1+2+3+4+......+99)
A=...................
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Tính nhanh các tổng sau:
a) D=1.4+2.5+3.6+..+100.103
b) E=1.3+2.4+3.5+...+97.99+98.100
Tính:
a,A=1.2+2.3+3.4+......+99.100
b,B=1.3+2.4+3.5+......+99.101
c,C=1.4+2.5+3.6+......+99.102
d,D=1.2.3+2.3.4+3.4.5+.......+98.99.100
\(A=1.2+2.3+3.4+...+99.100\)
\(\Rightarrow3A=1.2.3+2.3\left(4-1\right)+3.4\left(5-2\right)+...+90.100\left(101-98\right)\)
\(\Rightarrow3A=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+99.100.101-98.99.100\)
\(\Rightarrow3A=99.100.101\)
\(\Rightarrow A=\left(99.100.101\right):3\)
\(\Rightarrow A=333300\)
\(B=1.3+2.4+3.5+...+99.101\)
\(\Rightarrow B=1\left(2+1\right)+2\left(3+1\right)+3\left(4+1\right)+...+99\left(100+1\right)\)
\(\Rightarrow B=1.2+1+2.3+2+3.4+3+...+99.100+99\)
\(\Rightarrow B=\left(1.2+2.3+3.4+...+99.100\right)+\left(1+2+3+...+99\right)\)
\(\Rightarrow B=333300+4950\)
\(\Rightarrow B=338250\)
\(D=1.2.3+2.3.4+3.4.5+...+98.99.100\)
\(\Rightarrow4D=1.2.3.4+2.3.4.4+...+98.99.100.4\)
\(\Rightarrow4D=1.2.3\left(4-0\right)+2.3.4\left(5-1\right)+...+98.99.100\left(101-97\right)\)
\(\Rightarrow4D=1.2.3.4-0.1.2.3+2.3.4.5-1.2.3.4+...+98.99.100-97.98.99\)
\(\Rightarrow4D=98.99.100\)
\(\Rightarrow D=\left(98.99.100\right):4=242550\)
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