Respuesta :

Answer:

A

Step-by-step explanation:

[tex]s=\frac{a+b+c}{2}[/tex]

multiply both sides by 2

[tex]2s = a + b +c[/tex]

substract b and c from both sides to get a by itself

[tex]a = 2s - (b + c)\\a = 2s - b - c[/tex]

so the answer is A.