maka nila a adalah...

[tex]f(2x + 5) = (4x - 8)(2x + 3) \\ f(2x + 5) = 8 {x}^{2} - 4x - 24 \\ misal \: \: a = 2x + 5 \\ \: \: \: \: \: \: \: \: \: \: x = \frac{a - 5}{2} \\ jadi \\ f(a) = 8( \frac{a - 5}{2} )^{2} - 4( \frac{a - 5}{2} ) - 24 \\ = 2(a - 5)^{2} - 2(a - 5) - 24 \\ = 2 {a}^{2} - 22a + 36 \\ = {a}^{2} - 11a + 18 \\ f( - 9) = ( - 9)^{2} - 11( - 9) + 18 \\ = 198[/tex]