Question

1) Dada a função f(x)= x²-3x-4 calcule:
a) f(0)
b) f(-2)
c) f√2
d) f(-2/3)
e) f(x)=0

Answer 1

a) f(0)=0²-3(0)-4
f(0)=-4
b)f(-2)=(-2)²-3(-2)-4
f(2)=4+6-4
f(-2)=6
c)f(√2)=(√2)²-3(√2)-4
f(√2)=2-3√2-4
f(√2)=-2-3√2
d)f(-2/3)=(-2/3)²-3(2/3)-4
f(-2/3)=4/9-6/3-4
f(-2/3)=4/9-2-4
f (-2/3)=4/9-6
f(-2/3)=-50/9
e)x²-3x-4=0
∆=(-3)²-4.1.(-4)
∆=25
x'=3+5/2=4
x''=3-5/2=-1

Answer 2

 f(x)= x² - 3x - 4 calcule:
a)
 f(0) = 0² - 3.0 - 4
f(0) = 0 - 0 - 4
f(0) = - 4
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b)
f(-2) = (-2)² - 3.(-2) - 4
f(-2) = 4 + 6 - 4
f(-2) = 4 - 4 + 6
f(-2) = 6
-----------------------------------------
c)
f(√2) = (√2)² - 3.√2 - 4
f(√2) = 2 - 3√2 - 4
f(√2) = - 2 - 3√2
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d)
f(-2/3)

f(-2/3) = (-2/3)² - 3.(- 2) - 4
                              ( 3 )

f(-2/3) =  4 + 6 - 4
              9     3

f(-2/3) =  4 + 2 - 4
               9

f(-2/3) = 4 - 2
             9

f(-2/3) = 4 - 18
                9

f(-2/3) = - 14
                9

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e)
f(x) = 0
0 = x² - 3x - 4
x² - 3x - 4 = 0

a = 1; b = - 3; c = - 4

Δ = b² - 4ac
Δ = (-3)² - 4.1.(-4)
Δ = 9 + 16
Δ = 25

x = 3 + 5 = 8/2 = 4
         2

x = 3 - 5 = -2/2 = - 1
        2

R.: x = - 1 e x = 4