Persamaan garis yg melalui titik P(6,-7), dan tegak lurus dg garis 8y-12x=15 adalah

8y - 12x = 15
8y = 12x + 15
m = 12/8
m = 3/2

gradien saling tegak lurus
m1 . m2 = - 1
3/2 . m2 = - 1
m2 = - ⅔

pers garis
y - y1 = m ( x - x1 )
y + 7 = - ⅔ ( x - 6 )
y = - ⅔ x + 4 - 7
y = - ⅔ x - 3 ( dikali 3)
3y = - 2x - 9
3y + 2x = - 9