(15) diketahui f(2x-8)=x^2-4x. maka nilai dari f(6) adalah.

Cari inversnya terlebih dahulu
f(x) = y

[tex]y = 2x - 8 \\ 2x = y + 8 \\ x = \frac{y + 8}{2} \\ {f}^{ - 1} (x) = \frac{x + 8}{2} [/tex]
[tex]f(x) = ({ \frac{x + 8}{2} })^{2} - 4( \frac{x + 8}{2} ) \\ f(x) = \frac{ {x}^{2} + 16x + 64 }{4} - 2(x + 8) \\ f(x) = \frac{ {x}^{2} + 16x + 64}{4} - 2x - 16 \\ f(x) = \frac{ {x}^{2} + 16x + 64 - 4(2x - 16)}{2} \\ f(x) = \frac{ {x}^{2} + 1
8x }{2} [/tex]
Jika f(6)
[tex]f(6) = \frac{ {6}^{2} + 8(6)}{2} \\ f(6) = \frac{36 + 48}{2} \\ f(6) = 9 + 12 \\ f(6) = 21[/tex]