tolong pembahasannya dong min...

11) f(x) = 1/3x +4
y = 1/3x + 4
1/3x = y -4
x = (y -4).3
x = 3y - 12
f-(x) = 3x - 12
f-1(-2/3) = 3(-2/3)-12
= -2 -12
= -13
12) f(x) = 3x +7 dan g(x) = 3x^2 -5x +2
gof (-2/3) = g { f (-2/3) }
= g (3.-2/3 +7)
= g (-2 +7)
= g (5)
= 3(5)^2 -5.5 +2
= 75 -25 +2
= 52
13) 2x^2 - bx -7 = 0 salah satu akar -1, maka
2(-1)^2 - b(-1) -7 = 0
2 + b - 7 = 0
b = 5
maka PK : 2x2- 5x - 7 = 0
( x +1)(2x -7) = 0
akar yang lain => 2x - 7 = 0
2x = 7
x = 7/2