jika f(2x - 5) = x^2 + 3x - 1 maka nilai dari f(-11)... ?

Mapel : Matematika
Kelas : X SMA
Bab : Fungsi Komposisi dan Fungsi Invers

Pembahasan :
F(2x - 5) = x² + 3x - 1

Misal 2x - 5 = a
Maka x = (a + 5)/2

Substitusi keduanya...
f(a) = [(a + 5)/2]² + 3(a + 5)/2 - 1
f(-11) = [(-11 + 5)/2]² + 3(-11 + 5)/2 - 1
f(-11) = [(-6)/2]² + 3(-6/2) - 1
f(-11) = (-3)² + 3(-3) - 1
f(-11) = 9 - 9 - 1
f(-11) = -1

cara 1

2x - 5 = -11
2x = -11 + 5
x = -6 : 2
x = -3

f(-11) = (-3)² + 3(-3) - 1
f(-11) = 9 - 9 - 1
f(-11) = -1

cara 2

misal :
2x - 5 = a
x = (a+5) / 2

soal menjadi →
f(a) = (a+5 / 2)² + 3(a+5 / 2) - 1
f(a) = (a²+10a+25 / 4) + (3a+15 /2) - 1
f(a) = (a²+10a+25+6a+30-4) / 4
f(a) = (a² + 16a + 51) / 4

f(-11) = {(-11)² + 16(-11) + 51} / 4
f(-11) = (121 - 176 + 51) / 4
f(-11) = -4 / 4
f(-11) = -1

cara 1 dan cara 2 sama

semoga berguna +_+