Faça o estudo do sinal da função y = 3x+9 e indique para que valores de x a função é positiva, negativa ou nula:

a) positiva x>3, negativa x<3 e nula x=3

b) positiva x>-3, negativa x<-3 e nula x=-3

c) positiva x3 e nula x=3

d) positiva x-3 e nula x=-3

Correct option: b)

Step-by-step explanation:

To study the sign of the function, we have 3 cases:

Positive function: y>0

Negative function: y<0

Null function: y=0

Then, we just need to use the value of y in these inequations (or equation in the last case) to find the values of x:

Positive function: 3x + 9 > 0 - > 3x > - 9 - > x > - 3

Positive function: 3x + 9 3x x < - 3

Positive function: 3x + 9 = 0 - > 3x = - 9 - > x = - 3

Correct option: b)