tolong kerjakan yang no yang mana aj

1) a = 7
b = 10 - 7 = 3
Un = a + ( n - 1 ) b
U12 = a + ( 12 - 1 ) 3
= 7 + 11(3)
= 7 + 33
= 80

2) f(x) = ax + 5
f(6) = 6a + 5 = 17
6a = 17 - 5
6a = 12
a = 2
f(x) = 2x + 5
f(20) = 2(20) + 5 = 40 + 5 = 45

3) 2x + 4y = 6
4y = - 2x + 6
m = -2/4
m = - ½
sejajar m1 = m2 = - ½
pers garis
y - y1 = m ( x - X1 )
y - 5 = - ½ ( x - 3 )
y = - ½ x + 3/2 + 5 ( dikali 2 )
2y = - x + 3 + 10
2y + x = 13

4) 3x + 6y = 39
5x - 2y = 17 |×3
maka
3x + 6y = 39
15x - 6y = 51
--------------------(+)
18x = 90
x = 5
subtitusi
5x - 2y = 17
5(5) - 2y = 17
25 - 2y = 17
2y = 25 - 17
2y = 8
y = 4
nilai x + y
= 5 + 4
= 9