Salut!
[tex] \bf \{∡A,∡B,∡C\} \: d.p. \{5,8,5. \}[/tex]
[tex] \bf \: ∡A+∡B+∡C = 180°.[/tex]
[tex].....................................................................[/tex]
[tex] \bf \large \frac{∡A}{5} = \frac{∡B}{8} = \frac{∡C}{5} = k. ⇒ k = \frac{∡A+∡B+∡C}{5 + 8 + 5} = \frac{180}{18} = 10.[/tex]
[tex] \bf \frac{∡A}{ 5} =k⇒∡A=5 \times 10 = 50°.[/tex]
[tex] \bf \frac{∡B}{ 8} =k⇒∡B=8\times 10 = 80°.[/tex]
[tex] \bf \frac{∡C}{ 5} =k⇒∡C= 5 \times 10 = 50°.[/tex]
