diketahui f(x) = x² + 6x – 18. tentukan f-¹ (-11) ! jawab

f(x) = x² + 6x - 18
y = x² + 6x - 18
x² + 6x = y + 18
(x² + 6x + 9) = y + 18 + 9
(x + 3)² = y + 27
x + 3 = ± √y + 27
x = - 3 ± √x + 27
f-¹(x) = - 3 ± √x + 27

f-¹(-11)
= -3 ± √(-11) + 27
= -3 ± √16
= -3 ± 4
= 1 atau = -7