mohon jawabanya ya ,beserta caranya ,No 15-19

15) f(x) = mx + n
f(2) = 2m + n = 7
f(-1) = - m + n = - 2
---------------------------(-)
3m = 9
m = 3
subtitusi
- m + n = - 2
- 3 + n = - 2
n = - 2 + 3
n = 1
f(x) = mx + n
f(x) = 3x + 1
f(2) = 3(2) + 1 = 6 + 1 = 7 ( C )

16) A

17) m = ( y2 - y1 ) / ( x2 - X1 )
m = ( - 10 - 5 ) / ( - 2 - 1 )
m = - 15 / - 3
m = 5 ( D )

18) 2x - 3y + 4 = 0
- 3y = - 2x - 4
m = -2/-3
m = ⅔
gradien sejajar m1 = m2 = ⅔
pers garis
y - y1 = m ( x - X1 )
y + 5 = ⅔ ( x - 2 )
y = ⅔ x - 4/3 - 5 ( dikali 3)
3y = 2x - 4 - 15
3y - 2x = - 19
3y - 2x + 19 = 0
- 2x + 3y + 19 = 0
2x - 3y - 19 = 0

19) 3x + 2y = 8
x - y = 1 |×2
maka
3x + 2y = 8
2x - 2y = 2
----------------(+)
5x = 10
x = 2
subtitusi
x - y = 1
2 - y = 1
- y = 1 - 2
- y = - 1
y = 1
nilai 4x + 5y
= 4(2) + 5(1)
= 8 + 5
= 13 ( A )