10 = 9a + 3b + 1
9 = 9a + 3b/3
3 = 3a + b

jadi x = -b/2a

3 = -b/2a
6a = -b
b = -6a

Subtitusi

3a + b = 3
3a + (-6a) = 3

-3a = 3
a = -1

b = -6a
b = 6

Jadi a - -1 dan b = 6
F(x) = -x² +6x +1

Baca juga: Kunci Jawaban Matematika Kelas 9 Halaman 146 K13, Koordinat Titik Asal dan Bayangan

b. Fungsi f(x) mempunyai nilai minimum dengan nilai minimum –10 dan sumbu simetri x = 3.

Kunci Jawaban:

F(x) = ax² +bx + 1
-10 = a(3)² +3b + 1

-10 = 9a + 3b + 1
-11 = 9a + 3b

x = -b/2a
3 = -b/2a
6a=-b
b= -6a

9a + 3b = -11
9a + 3(-6a) = -11
9a - 18a = -11
-9a = -11
a = 11/9