Question

1.Diketahui f(x)=5x-9.
Nilai f(2a+1)+f(3) adalah ....

2.Diketahui f(x)=ax+b.jika f(4)=-3 dan f(-2)=9 nilai f(6) adalah.....

Answer 1

1.
f(x) = 5x -9
f(2a+1) = 5(2a+1) -9 = 10a -4
f(3) = 5.3 -9 = 15-9 = 6
jadi
f(2a+1)+f(3) = 10a -4 +6= 10a+2

2.
f(x) = ax+b
f(4) = 4a+b = -3.......(pers 1)
f(-2) = -2a+b = 9......(pers 2)

disub dengan nilai b = -4a-3 ke pers 2
-2a+ (-4a-3) = 9
-6a = 12
a = -2 disub ke pers 1
4(-2)+b = -3
-8 +b = -3
b = 5

jadi
f(x) = -2x + 5
f(6) = -12 + 5 = -7

Answer 2

1).

f(x) = 5x - 9
f(2a+1) + f(3) = ( 5 ( 2a + 1 ) - 9 ) + ( 5 ( 3 ) - 9 )
                      = ( 10a + 5 - 9 ) + ( 15 - 9 )
                      = ( 10a - 4 ) + 6
                      = 10a + 2

2).

Cari nilai a :
( 9 + 3 ) : ( -2 - 4 ) = 12 : -6 = -2

Cari nilai b :
f(4) = -3
  -3 = -2(4) + b
  -3 = -8 + b
   b = 5

Sehingga,
f(6) = -2(6) + 5
       = -12 + 5
       = -7