tolong jawab soal nomor 18,19,dan 20 ya...

18) Mp = -3/2 tegak lurus Mq = 2/3 (C)

19)
# M = -koefisien x/koefisien y
= -5/-4
= 5/4

# y-y1 = m (x-x1)
y-(-3) = 5/4 (x-2)
4(y+3) = 4 . 5/4 (x-2)
4y+12 = 5x-10
-5x+4y = -10-12
-5x+4y = -22 (semuanya dikali -1)
5x-4y = 22 (A)

20) # Eliminasi y
x+2y = -1 (dikali 2)
3x-4y = 17 (dikali 1)

2x+4y = -2
3x-4y = 17
_________+
5x = 15
x = 15/5
x = 3

#Substitusi x
x+2y = -1
3+2y = -1
2y = -1-3
2y = -4
y = -4/2
y = -2

#a=x dan b=y

# 2a-b
= 2 . 3 - (-2)
= 6 + 2
= 8 (D)