Question

[Lê Mạnh Hùng]

tìm các số nguyên a, b thỏa mãn : a/3-4/b=1/5

Answer 1

[Hacker♪]

Ta có :a3−4b=15a3−4b=15

=> ab−123b=15ab−123b=15

=> 5ab - 60 = 3b

=> 5ab - 3b = 60

=> b(5a - 3) = 60 

Answer 2

[Green sea lit named Wang Junkai]

$\frac{\mathrm{a\; =\; x}}{}$

$\frac{\mathrm{b=y}}{}$

$\frac{x}{3}-\frac{4}{y}=\frac{1}{5}$

$\iff \frac{x}{3}-\frac{1}{5}=\frac{4}{y}$

$\iff \frac{5x}{15}-\frac{3}{15}=\frac{4}{y}$

$\iff \frac{5x-3}{15}=\frac{4}{y}$

$\iff \left(5x-3\right)y=15.4$

$\iff \left(5x-3\right)y=60$

Vì $x,y\in Z\iff 5x-3\in Z;5x-3;y\in Ư\left(60\right)$

$5x-3⋮5/$

Xét ước là ra!