How many four-digit numbers can you form from the numbers 1, 2, 3, 4, 5, 6, 7, 8, and 9 (a) if you use each digit only once? (b) if you can repeat each digit?

answer: the product of the slopes of perpendicular lines = -1

if   the slope of the line is m then the slope of the perpendicular line = -1/m

here the line y = -10x + 1 has a slope of -10 so the slope of the perpendicular line is -1/-10 = 1/10

this perpendicular line passes through the point (5, 7) and we know the slope so we can find the equation of the line since it will also pass through the point (x, y)

using the point slope formula for the equation of the line

(y - 7) = 1/10(x - 5)   same as y = 1/10x -5/10+ 7

we can rewrite this to the form ax + by = c to get

1/10x + y = 13/2

the second and third options posted are the same. i think one should have a positive 13/2

step-by-step explanation: