In the xy-coordinate system, points (2, 9) and (-1, 0) lie on line k. if the point (n, 21) lies on line k, what is the value of n?
a. 6
b. 7
c. 8
d. 9
e. 10

A

Step-by-step explanation:

Since they lie on the same line, it means that they are collinear.

Since they are collinear, the value of the slope between each 2 point is the same. Hence, we can have points PQR with the slopes PQ, PR and QR being the same.

The general formula for finding the slope of a line with 2 end points is :

m = (y2 - y1)/(x2 - x1)

using the first two points,

m = (0 - 9)/-1 -2 = -9/-3 = 3

Now to get the value of n. We can use the second point and the point containing n.

This means:

3 = (21 - 0)/(n + 1)

3 = 21/n + 1

3n + 3 = 21

3n = 18

n = 6

b) 36

step-by-step explanation:

18 times 2 is 36

y = 5x + 17

step-by-step explanation:

a perpendicular line will be the opposite reciprocal slope of the given equation.   the slope given is -1/5 so the opposite reciprocal is 5

find b:

7 = 5 (-2) + b

7 = -10 + b

17 = b

write equation

y = 5x + 17