Question

A função y = - x2 + 3 x + 4 tem sinal positivo no intervalo:  

Answer 1

y = -x² + 3x + 4
Δ = b² - 4ac
Δ = 9 - 4(-1)(4) = 25
x = ( - b +- √Δ) / 2a
x =( -3 +- 5) / -2
x1 = 4
x2 = -1

-1 < x < 4

Answer 2

x=-3+-√9-4.(-1).4/-2
x=-3+-√9+16/-2
x= -3+-√25/-2
x= -3+-5/-2
x1= -3+5/-2= 2/-2= -1
x2= -3-5/-2= -8/-2= 4