tim cac stn n sao cho n+1;n+3;n+7;n+9;n+13;n+15 la so nguyen to
tim tat ca cac stn n sao cho ( 3n + 1 ) la 1 so chinh phuong
tim tat ca cac stn co 3cs abc sao cho abc =n^2-1va cba=(n-2)^2
tim cac stn n sao cho : a) n2 +2n +6 chia het cho n+4.
b) n2 + n+ 1 chia het cho n+1
Tim cac stn n biet:5n+45 chia het cho n+3
5n+45 ⋮ n+3
=> [(5n+15)-15+45] ⋮ n+3
=> [(5n+3.5)+30] ⋮ n+3
=> [5.(n+3)+30] ⋮ n+3
có n+3 ⋮ n+3 => 5.(n+3) ⋮ n+3
=> 30 ⋮ n+3
=> n+3 ∈ Ư(30)
=> n+3 ∈ {1;2;3;5;6;10;15;30} mà n ∈ N
=> N ∈ {0;2;3;7;12;27}
vậy_____
Tim STN n lon nhat sao cho so 2015 bang tong cua n so a1,a2,a3,...,an trong do tat ca cac so a1,a2,a3,...,an deu la hop so
tim STN n de cac bieu thuc sau la STN : B= 2n+2/n+2 + 5n+17/ n+2 - 3n/ n+2
bai 1 tim cac stn x y z sao cho x+y+z=xyz
bai 2cmr neu m^2+mn+n^2chia het cho 9 voi m ,n la cac stn thi m,n chia het cho 3
bai 3 tim stn n nho nhat de cac phan so sau toi gian
7/n+9.8/n+10,...,31/n+33
bai 4chung to rang phan so m^3+2m/m^4+3m^2 +1 toi gian
bai 5 a,cmr khong ton tai so chinh phuong nao co dang abab
b,cho 51 so nguyen duong khong vuot qua 100 cmr ton tai 2 so trong 51 so noi tren ma 1 so chia het cho so con lai
c,tim cac so co 3 chu so sao cho hieu cua so ay va gom 3 chu so ay viet theo thu tu nguoc lai la mot so chinh phuong
bai 6cmr A=2x(x+y-1)+y^2+1 luon nhan gia tri khong am voi moi x,y
bai 7 tim hai so nguyen duong sao cho tong ,hieu thuong (so lon chia cho so nho )cua chung cong lai duoc 38
bai 8 cho ba so a,b,c thoa man a/2009=b/2010=c/2011
tinh gia tri cua bieu thuc M=4(a-b)(b-c)-(c-a)^2
Tim tat ca cac STN co dang abc sao cho abc = n2 va cba = ( n + 2 ) 2 -1
1,Tim STN n sao cho n + 4 chia het cho n + 1
n+4 chia hết cho n+1
n+1+3 chia hết cho n+1
=>3 chia hết cho n+1 hay n+1EƯ(3)={1;3}
=>nE{0;2}