Tìm hai số tự nhiên a,b.Biết ƯCLN(a,b)=1 ; BCNN(a,b)=10
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Gọi a; b là 2 số cần tìm với a>b
ƯCLN(a;b)=6
Vậy ta có: a=6m; b=6n với ƯCLN(m;n)=1
Vì a.b=216 nên 6m.6n=216 suy ra m.n=6. Do m;n là nguyên tố cùng nhau nên ta lập được bảng:
m | 1 | 6 | 3 | 2 |
n | 6 | 1 | 2 | 3 |
a | 15 | 90 | 45 | 30 |
b | 90 | 15 | 30 | 45 |
Vì a>b nên có 2 trường hợp:
1) a=90 thì b=15
2) a=45 thì b=30
vì ƯCLN(a,b)=6 (a<b)
a=6m
b=6n
với (m,n)=1,m\(\le\)n
a+b=6m+6n=6(m+n)=84
=>m+n=14
m=1 ,n=13,=>a=6,b=78
m=3,n=11,=>a=18,b=66
m=5,n=9,=>a=30,b=54
m=7,n=7,a=42,b=42
bài còn lại cũng tương tự
a) goi hai so la a ; b va a >b
vi UCLN(a,b)=18=>a=18k ; b=18q (trong do UCLN (k,q)=1 va k>q)
=>a+b=162
18k+18q =162
18(k+q)=162
k+q=9
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