Gọi UCLN(21n+4,14n+3)=d
Ta có: 21n+4 chia hết cho d => 2(21n+4) chia hết cho d => 42n+8 chia hết cho d
14n+3 chia hết cho d => 3(14n+3) chia hết cho d => 42n+9 chia hết cho d
=> 42n+9-(42n+8) chia hết cho d
=> 1 chia hết cho d
=> d=1 (dpdcm)
bai 1:tim n thuoc n de:3(n+2) chia het cho n-2
bai 2chng minh rang cac so sau la cac so nguyen to cung nhau
a) 18n+3 va 21n+4
b)2n+1va3n+1
bai 3:tim hai so biet tong hai so la 90 va uoc chung lon nhat la 15
bai 4:tim so tu nhien n lon nhat co 3 chu so sao cho n :15 du 9va n:35 du 29
bai 5:tim uoc chung lon nhat cua cac so sau:
a)18n+3 va 21n+4
b)9n+13 va 3n+4
bai 6:chung minh: voi moi a,b thuoc nta co
UCLN(a,b)=UCLN (5a+2b,7a+3b)
AI DUNG TRUOC 9H MINH SE TICH CHO.THANHK YOU VERY MUCH!
tim 2 so tu nhien a va b biet tich cua chung =210 biet rang voi 2 so tu nhien ab, ta co a.b= uoc chung lon nhat
chung minh rang voi moi so tu nhien n # 0 thi:
a moi so nguyen to lon hon 2 deu co dang 4n _+1
b moi so nguyen t lon hon 3 deu co dang 6n +_1
voi n so tu nhien thoa man 6n+1 va 7n-1 la hai so tu nhien khong nguyen to cung nhau thi uoc chung lon nhat cua 6n+1 va 7n-1 la bao nhieu
chung minh rang : voi moi so tu nhien n thi (n+5).(n+10) chia het cho 2
chung minh rang voi moi so tu nhien n thi n^2 + n + 6 khong chia het cho 5
giup to voi no khung qua
tim 2 so tu nhien biet tong uoc chung lon nhat va boi chung nho nhat la 23
chung minh rang voi moi so tu nhien n thi tich (n+2)(n+5) la mot so chan
tim uoc chung lon nhat cua tat ca cac so tu nhien co 6 chu so gom cac chu so tu 1 den 6
