Tìm hai số a và b (a<b) ,biết :ƯCLN(a;b) =10 BCNN(a;b) =900
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- Ta có: a ≥ b ( a,b ∈ N )
ƯCLN ( a, b) = 16
⟹ a chia hết cho 16 ⟹ a = 16.m
⟹ b chia hết cho 16 ⟹ b = 16. n
(m, n là thương; m,n ∈ N, m ≥ n)
ƯCLN(m,n) = 1
⟹ a . b = ƯCLN.BCNN
mà a = 16. m
b = 16. n
Thay số: 16 . m . 16 . n = 16 . 240
16. m . 16. n = 3840
256. m. n = 3840
⟹ m. n = 3840 : 256 = 15
Ta có bảng sau :
m | ... | ... | ... |
n | ... | ... | ... |
a | ... | ... | ... |
b | ... | ... | ... |
⟹ Vậy (a,b) ∈ { (... , ...) ; (... , ....)}
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
ta co bang sau | |||||||||||||||||||||||
vay ........... | |||||||||||||||||||||||
21453
52542000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 | 542454550212.100000000000000000000000000000000000000000000000000000000000000000000000000000 |
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