A=1.2+2.3+3.4+...+2002.2003
Tính A?
Tính
a) S= 1.2+2.3+3.4+...+32.33
b) S= 1.2+2.3+3.4+...+49.50
Ta có : S = 1.2 + 2.3 + 3.4 + ..... + 32.33
=> 3S = 1.2.3 - 1.2.3 + 2.3.4 - 2.3.4 + ...... + 32.33.34
=> 3S = 32.33.34
=> S = \(\frac{32.33.34}{3}=11968\)
Cho A=1/1.2 + 1/2.3 + + 1/ 3.4+...+1/49.50 ; B = 1.2+2.3+3.4+4.5+5.6+...+49.50
Tính 50 mủ 2 A – B/17
A= 1.2+2.3+3.4+...........+ 2020.2021
A=1.2+2.3+3.4+...+99.100
3S=1*2*3+2*3*(4-1)+...+99*100*(101-98)
=1*2*3+2*3*4-1*2*3+...+99*100*101-99*100*98
=99*100*101
=>S=33*100*101=333300
A=1.2+2.3+3.4+...+98.99.Tính A
Số các số hạng của A là :
( 99 - 1 ) : 1 + 1 = 99 ( số )
Tổng A là :
( 99 + 1 ) . 99 : 2 = 4950
Vậy tổng A = 4950 .
Mk ko ghi lại đề bài mà làm tiếp luôn nhé!
3A=1.2.3+2.3.3+3.4.3+.......+98.99.3
3A=1.2.3+2.3.(4-1)+3.4.(5-2)+.........+98.99.(100-97)
3A=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+..............
3A=98.99.100
A=98.99.100/3
Bn k cho mk nhé!
B=
A = 1.2+2.3+3.4+.........................+1999.2000
A = 1.2+2.3+3.4+.........................+1999.2000
=> 3A= 1.2.(3-0) + 2.3.(4-1) + ... + 1999.2000(2001-1998)
=> 3A=1.2.3+2.3.4-1.2.3+...+1999.2000.2001-1998.1999.2000
=> 3A=1999.2000.2001
A=1999.2000.2001:3=2666666000
A=1.2+2.3+3.4+...+123.124= ?
=> 3A = 1.2.3 + 2.3.3 + 3.4.3 + ...+ 123.124.3
3A = 1.2.(3 - 0) + 2.3.(4 - 1) + 3.4.(5 - 2) + ... + 123.124.(125 - 122)
3A = 1.2.3 - 1.2.0 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + ...+ 123.124.125 - 122.123.124
3A = 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + ...+ 123.124.125 - 122.123.124
3A = 123.124.125
=> A = \(\frac{123.124.125}{3}=635500\)
A= 1.2+2.3+3.4+......+ 49.50
A = 1.2 + 2.3 + ........+49.50
3A = 1.2.(3-0) + 2.3.(4-1)+........+49.50.(51 - 48)
3A = 1.2.3 + 2.3.4 - 1.2.3 +........ + 49.50.51 - 48.49.50
3A = 48.49.50 = 117600
A = 39200
Ta có :
Gọi A=1.2+2.3+3.4+4.5+...+49.50
A=1.2+2.3+3.4+4.5+...+49.50
3.A=3.(1.2+2.3+3.4+4.5+...+49.50)
3.A=1.2.3+2.3.3+3.3.4+3.4.5+...+3.49.50
3.A=1.2.(3-0)+2.3.(3-0)+(3-0).3.4+(3-0).4.5+...+(3-0).49.50
3.A=1.2.3-0+2.3.3-0+3.3.4-0+3.4.5-0+...+3.49.50-0
3.A=1.2.3-0+2.3.4-1.2.3+5.3.4-2.3.4+...+49.50.51-48.49.50
3.A=49.50.51
A= 49.50.51/3
A= 49.50.17.3/3
A=49.50.17
A=41650
Đáp số : A=41650
1x2+2x3+3x4+4x5+...+49x50=A
3.(1.2+2.3+3.4+4.5+...+49.50)=A.3
3.1.2+3.2.3+3.3.4+3.4.5+...+3.49.50+A.3
(3-0).1.2+(4-1).2.3+(5-2).3.4+(6-3).4.5+...+(51-48).49.50=A.3
3.1.2-0.1.2+4.2.3-1.2.3+5.3.4-2.3.4+6.4.5-3.4.5+...+51.49.50-48,49,50=A.3
51.49.50=A.3
51.49.50:3=A
các bạn cứ tính kết quả ra là ok
A=1.2+2.3+3.4+...+2018.2019
\(A=1.2+2.3+3.4+...+2018.2019\)
\(3A=1.2.3+2.3.3+3.4.3+...+2018.2019.3\)
\(3A=1.2.3+2.3.\left(4-1\right)+3.4.\left(5-2\right)+...+2018.2019.\left(2020-2017\right)\)
\(3A=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+2018.2019.2020-2017.2018.2019\)
\(3A=2018.2019.2020\)
\(A=2018.673.2020\)
\(A=2743390280\)
Chúc bạn học tốt ~
Đặt A = 1x2 + 2x3 + 3x4 + ... + 99 x 100
3A = 1x2x3 + 2x3x3 + ... + 99x100x3
3A = 1x2x( 3 - 0 ) + 2x3x(4 - 1 ) +...+ 99x100x(101 - 98)
3A = ( 1x2x3 + 2x3x4 + ... + 99x100x101 ) - ( 0x1x2 + 1x2x3 +...+ 98x99x100)
3A = 99x100x101 - 0x1x2
3A = 99x100x101 - 0
A = 99x100x101 : 3
A = 333300
Vậy A = 3333000
A=1.2+2.3+3.4+...+50.51