TERBARU KUNCI JAWABAN Matematika Kelas 9 Semester 1 Halaman 102 Latihan 2.3 Sumbu Simetri dan Titik Optimum

Jawaban:

U1 = 0
a(1²) + b(1) + c = 0
a + b + c = 0
c = -a – b

U2 = -9
a(2²) + b(2) + c = -9
4a + 2b + c = -9
4a + 2b + (-a – b) = -9
3a + b = -9

U3 = -12
a(3²) + b(3) + c = -12
9a + 3b + (-a – b) = -12
8a + 2b = -12 (bagi 2)
4a + b = -6

eliminasi
3a + b = -9
4a + b = -6
—————— _
-a = -3
a = 3

3(3) + b = -9
9 + b = -9
b = -18

c = -3 – (-18) = 15

Un = 3n² – 18b + 15

nilai minimum turunan = 0
6n – 18 = 0
6n = 18
n = 3

maka nilai minimum saat n = 3
maka nilai minimum U3 = -12