Question

Tìm a , b thuộc Z\(\frac{9}{56}\)< \(\frac{a}{8}\)<\(\frac{b}{7}\)<\(\frac{13}{28}\)

Answer 1

Ta có: \(\frac{9}{56}<\frac{a}{8}<\frac{b}{7}<\frac{13}{28}\)

=> \(\frac{9}{56}<\frac{7a}{56}<\frac{8b}{56}<\frac{26}{56}\)

Nếu \(a=2\)thì \(b=3\)

Answer 2

Ta có : \(\frac{9}{56}<\frac{a}{8}<\frac{b}{7}<\frac{13}{28}\)

=> \(\frac{9}{56}<\frac{7a}{56}<\frac{8b}{56}<\frac{26}{56}\)

=> \(9<7a<8b<26\)

Vì a, b ∈ Z => 7a, 8b ∈ Z

=> 7a, 8b ∈ { 10 ; 11 ; 12 ; 13 ; 14 ; 15 ; 16 ; 17 ; 18 ; 19 ; 20 ; 21 ; 22 ; 23 ; 24 ; 25 }

=> 7a ∈ { 14 ; 21 } ; 8b ∈ { 16 ; 24 }

- Khi 7a = 14 => a = 2

- Khi 7a = 21 => a = 3

- Khi 8b = 16 => b = 2

- Khi 8b = 24 => b = 3