Tìm hai số tự nhiên và () có BCNN bằng và ƯCLN bằng .
Đáp số: và .
Giúp mình
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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 BCNN(a,b)=300 và ƯCLN(a,b)=15
⇒a.b=300.15=4500
vì ƯCLN(a,b)=15 nên a=15m và b=15n(với ƯCLN(m,n)=1)
vì a+15=b⇒15m+15=15n
mà a.b=4500nên ta có: 15m.15n=4500
15.15.m.n=4500
\(15^2\).m.n=4500
225.m.n=450
⇒m.n=20
⇒m=1 và n=20 hoặc m=4 và n=5
mà m+1=n⇒m=4 và n=5
vậy a=15.4=60 và b=15.5=75
vì a*b=UCLN*BCNN của a và b
=>a*b=15*300=4500
ta có hệ:\(\int^{a\times b=4500}_{a-b=15}\)
giải hệ ta đc:a=±75
b=±60
ƯCLN(a,b)=\(\frac{ab}{BCNN\left(a,b\right)}\)
=>15=\(\frac{ab}{300}\)
=>ab=15.3000=4500
=>a,b là Ư(4500)={1;45;.....;60;75;.....100;45}
a | 45(loaị) | ... | 75(thỏa mãn) |
b | 1 | .... | 60 |
Lời giải:
Vì ƯCLN của a,b là $15$ nên đặt $a=15x, b=15y$ với $(x,y)=1$ và $1< x< y$
Khi đó:
BCNN(a,b) = $15xy=525$
$\Rightarrow xy=35$
Vì $(x,y)=1$ và $1< x< y$
$\Rightarrow (x,y)=(5,7)$
$\Rightarrow (a, b) = (15.5, 15.7) = (75, 105)$