persamaan parabola y = ax² + bx +c melalui titik titik (1,2) ,(2,4) (3,8).persamaan parabola tersebut adalah... a. y=X² + X + 2 b. y = X² + X - 2 c. y = X² - X

y = ax² + bx + c

titik ( 1,2)
2 = a ( 1)² + b(1) + c
2 = a + b + c ... pers 1

titik ( 2,4 )
4 = a ( 2)² + b ( 2) + c
4 = 4a + 2b + c .. pers 2

titik ( 3,8)
8 = a ( 3)² + b ( 3) + c
8 = 9a + 3b + c ... pers 3

pers 1 & 2
a + b + c = 2
4a + 2b + c = 4
----------------------(-)
- 3a - b = - 2 ...pers 4

pers 1 & 3
a + b + c = 2
9a + 3b + c = 8
-----------------------(-)
- 8a - 2b = - 6 ... pers 5

pers 4 & 5
- 3a - b = - 2 |×2
- 8a - 2b = - 6
maka
- 6a - 2b = - 4
- 8a - 2b = - 6
---------------------(-)
2a = 2
a = 1

subtitusi
- 3a - b = - 2
- 3(1) - b = - 2
- 3 - b = - 2
- b = - 2 + 3
- b = 1
b = - 1

subtitusi
a + b + c = 2
1 - 1 + c = 2
c = 2

pers parabola
y = ax² + bx + c
y = x² - x + 2 ( C )