Question

Doar exercitiile cu punct rosu!

Answer 1

3. ab + ca = 715 (il dam factor comun pe 'a')

a × (b + c) = 715 |×5 (inmultim relatia cu 5)

a × 5 × (b + c) = 715 × 5

a × (5b + 5c) = 3575 |×18 (inmultim relatia cu 18)

18 × a × (5b + 5c) = 18 × 3575

=> 18a (5b + 5c) = 64350

9. A = { 2x + 1 | x ∈ N, x ∈ D₁₀ }

=> x ∈ D₁₀ = {1, 2, 5, 10}

2 × 1 + 1 = 3

2 × 2 + 1 = 5

2 × 5 + 1 = 11

2 × 10 + 1 =21

=> A = { 3, 5, 11, 21 }

10. B = { 2x + 3 | x = cifra para}

=> x ∈ { 0, 2, 4, 6, 8 }

2 × 0 + 3 = 3

2 × 2 + 3 = 7

2 × 4 + 3 = 11

2 × 6 + 3 = 15

2 × 8 + 3 = 19

=> B = { 3, 7, 11, 15, 19 }

11. ( 2a - 3 ) × 6 = 54 - 6a |:6 (impartim relatia la 6)

2a - 3 = 9 - a

3a = 12

=> a = 4

Cerintele de la exercitiile '2' si '4' sunt gresite!