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16 tháng 3 2020
b1
ta có : n+4 = (n+1)+3
=>n+1+3 chia hết cho n+1
vì n+1 chia hết cho n+1
=>3 chia hết cho n+1
=> n+1 chia hết cho 3
=> n+1 thuộc Ư 3 =[1;3]
=> n+1=1 n+1=3
n =1-1 n =3-1
n =0 n =2
vậy n thuộc [0;2]
14 tháng 10 2018
Bo may la binh day k di hieu ashdbfgbgygygggydfsghuyfhdguuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu3
M = 40 + 41 + 42 + 43 + ... + 498
=> 4M = 41 + 42 + 43 + 44 + ... + 499
Khi đó 4M - M = (41 + 42 + 43 + 44 + ... + 499) - (40 + 41 + 42 + 43 + ... + 498)
=> 3M = 499 - 40 = 499 - 1
Khi đó 2x = 3M + 1
<=> 2x = 499 - 1 + 1
=> 2x = 499
=> 2x = (22)99
=> 2x = 22.99
=> 2x = 2198
=> x = 198
Vậy x = 198
M = 40 + 41 + 42 + 43 + ... + 498
4M = 4( 40 + 41 + 42 + 43 + ... + 498 )
= 41 + 42 + 43 + 44 + ... + 499
=> 3M = 4M - M
= 41 + 42 + 43 + 44 + ... + 499 - ( 40 + 41 + 42 + 43 + ... + 498 )
= 41 + 42 + 43 + 44 + ... + 499 - 40 - 41 - 42 - 43 - ... - 498
= 499 - 1
2x = 3M + 1
<=> 2x = 499 - 1 + 1
<=> 2x = 499
<=> 2x = (22)99 = 2198
<=> x = 198