{a,b} direct proporționale {2,7}
b-a=15
a=?
b=?

a/2 = b/7 = k

a = 2k

b = 7k

b - a = 15

7k - 2k = 15

5k = 15

k = 3

a = 2k = 6

b = 7k = 21

[tex] \{a,b \} \: \: d.p. \: \: \{2,7 \} \\ \it b - a = 15 \\ \frac{a}{2} = \frac{b}{7} = K \\ \\ \it \frac{a}{2} = K \: = = > a = 2K \\ \\ \frac{b}{7} = K = = > b = 7K \\ \\ 7K - 2K = 15 \\ \it 5K = 15 \\ \\ K = \frac{15}{5} \\ \\ \it K = 3 \\ \it a = 2K = = > a = 2 \cdot 3 = = > \mathbf{a = 6} \\ b = 7K = = > b = 7 \cdot 3 = = > \mathbf{b = 21}[/tex]