1. diket f(x) = x² + ax + 5 jika f(2) = 21 tentukan f(-3)?

Jawab:

nilai  fungsi

1. diket f(x) = x² + ax + 5 jika f(2) = 21 tentukan f(-3)?

jawab :

f(2) = 21

2² + a(2) + 5= 21

4 + 2a +  5= 21

2a + 9 = 21

2a= 12

a=  6

f(x)=  x² + 6x + 5

f(3) =  3²+6(3) + 5

f(3)=  9 + 18 +  5

f(3) = 32

2. diket f(x) = x² + ax + b jika f(4) = f(-3) = 0 tentukan f(2)?

jawab :

f(4) = 0

4²+a(4) + b = 0

16 + 4a + b = 0

4a+ b  = – 16

f(-3) = 0

(-3)²+ a(-3) + b = 0

9 -3a +  b = 0

-3a + b = – 9

eliminasi

4a+ b =  -16

-3a + b = -9   –

7a = – 7

a= – 1

4a + b  = -16

4(-1) + b = – 16

-4 + b = – 16

b = – 16 +  4

b = – 12

f(x) = x² –  x    - 12

f(2) = 2² – 2 -12

f(2) =  4 -2 – 12

f(2) = -10

3. diket f(x) = x² + ax + b jika f(2) = -8 dan f(4) = 0 tentukan f(1)?

jawab :

f(-2)= – 8

(-2)²+ a(-2) + b = -8

4 – 2a + b = -8

-2a + b = – 4

f(4)= 0

4²+ a(4) + b = 0

16+ 4a + b= 0

4a+ b = -16

eliminasi

-2a + b = -4

4a +  b = – 16   (-)

-6a  = 12

a= – 2

-2a + b = – 4

-2(-2) + b = – 4

4 + b = – 4

b = -4 – 4

b = – 8

f(x) =  x² – 2x –  8

f(1) =  1² – 2(1)-  8

f(1)= 1 – 2 – 8

f(1) = – 9